Testing the BluOS Wireless System with a NAD Masters M66 Streaming Preamplifier and PSB ALPHA IQ Wireless Speakers

BluOS is a streaming ecosystem that can support bitrates up to 24/192 lossless. It was released by The Lenbrook Group in 2013 and is compatible with FLAC (Free Lossless Audio Codec), MQA (Master Quality Authenticated), WAV, AIFF, ALAC, AAC, and MP3 (for compatibility). It is available on Lenbrook brands, including NAD electronics and PSB Speakers.

Since SECRETS had received a NAD Masters M66 Streaming Preamplifier and a pair of PSB Alpha iQ Bookshelf Speakers for review, I decided to test BluOS’ capabilities on these components.

NAD and PSB Speakers are part of the Lenbrook Group and several of their products are BluOS-capable. BluOs is not a codec (although MQA processing is embedded in its architecture) or a streaming service. It is a streaming platform that aggregates and integrates several online streaming sources and services and combines it with the ability to control several BluOs enabled devices (whether wired or wireless) on a home network to establish a household streaming ecosystem with App control. Unlike ROON BluOs is more of a closed ecosystem and works only with BluOs-enabled devices.

SECRETS reviewed the NAD Masters M33 integrated amplifier in 2021 and found it to be a wonderful and flexible piece of kit. The new NAD Masters M66 is somewhat like taking the preamp section of the M33 and putting it on steroids. It is designed for better performance and improved flexibility. With the Inclusion of DIRAC Live (Full Frequency) room correction and DIRAC Live Bass Control (Full version), it is the only HIFI component that can blend up to four independent subwoofers into a “traditional” 2-channel audio system. A true audio “central nervous system” if you will.

It is designed to go with their M23 Power Amplifier which is shown in the photo below.

PSB’s Alpha iQ Bookshelf Speakers, like the M66, are BluOS-enabled. They are designed to be all you need for a fun, compact, and powerful high-res music streaming system. All you need is your smartphone with the BluOs app installed, a wired or wireless internet connection, and a couple of power outlets. That’s it. There isn’t even a connection cable that runs between the two speakers as they communicate wirelessly with each other. The BluOs app allows your phone to act as a supercharged remote control coordinating access to a multitude of streaming services and music files stored on any USB drive connected to the speakers. Music is streamed directly to the Alpha iQ from file locations and music services ensuring lossless transmission. No music is routed through the smartphone unless you are intentionally using the Bluetooth connection and streaming audio directly from your phone as a source. The speakers also have an HDMI eARC input for use with a TV and an MM phono input if one is ever in a vinyl frame of mind. The Alpha iQ comes in a large variety of colors to go with any décor or mood. We received a pair in the Matte White finish.

Please note that this is simply an introductory article about these two pieces of equipment. I am mostly focusing on my experience using the BluOs system with the NAD M66 and the PSB Alpha iQ speakers. Since I consider objective measurements very important, I felt I needed to run a series of bench tests on the NAD M66 to objectively assess some of its performance capabilities. You will find those below.

A full review of each component delving into many more of their individual details will be coming soon courtesy of Isaac Adams (M66) and Jeff Wheaton (Alpha iQ).

LINE IN, SINGLE-ENDED / ANALOG AUDIO OUTPUT

BALANCED IN, BALANCED / ANALOG AUDIO OUTPUT

DIGITAL SOURCE IN, SINGLE-ENDED / ANALOG AUDIO OUTPUT

DIGITAL SOURCE IN, BALANCED / ANALOG AUDIO OUTPUT

LINE IN, SINGLE-ENDED / SUBWOOFER OUTPUT/ 2 SUBWOOFERS

BALANCED IN, BALANCED / SUBWOOFER OUTPUT / 2 SUBWOOFERS

PHONO INPUT, SINGLE-ENDED / ANALOG AUDIO OUTPUT (Analog bypass)

LINE INPUT, HEADPHONE OUT (Analog Bypass)

BluOS

AUDIO

CONNECTIONS

DIMENSIONS AND WEIGHT

GENERAL SPECIFICATIONS

The NAD Masters M66 Streaming Preamplifier uses one of ESS’s highest-quality Sabre DAC chips, the ES9038PRO. An ESS ES9822PRO ADC (Analog-to-Digital Converter) chip is used in the Analog Direct XLR and RCA inputs. The ADC can be bypassed for a pure analog signal to pass through, this negates the use of DIRAC or the balance and tone controls in that case. The other inputs are all digital and pass through the DAC.

The front has a 7″ touchscreen for scrolling through the menu. The volume control on the right has 100 steps.

The rear panel of the M66 is shown below. Click on the photo to see a large version. You can see the vast array of digital inputs including AES/EBU (XLR) which is a balanced input. Analog inputs include one pair of XLR balanced, two pairs of RCA single-ended, and a pair of RCA single-ended inputs for the phono preamp MM and MC circuits. Analog outputs include one pair of XLR balanced and one pair of RCA single-ended. There are four XLR-balanced analog subwoofer outputs. All inputs pass through the DAC for DSP features such as Dirac Live Room Correction and Bass Control, Tone Controls, and Bass Management (the latter feature uses the four sets of XLR subwoofer outputs). Additionally, there is an HDMI input (with eARC) if you want to extract a stereo signal from a modern TV, and the requisite trigger sockets. There are two MDC2 expansion slots on the left which are available for future new features.

BluOS, will allow up to 24-bit/192 kHz uncompressed audio to the new PSB Alpha iQ Bookshelf Speakers. The ¾-inch aluminum dome tweeter is positioned underneath the 4-inch polypropylene woofer, which is an unconventional layout. According to PSB, there is a very good reason for this.

“By placing the tweeter below the woofer, with typical bookshelf speaker placement, the arrival time for both woofer and tweeter is closer than if it were in more typical driver placement. The benefit is better phase coherency, thus improved imaging and fine dynamics.”

You can’t turn them over because a push button control is on the top of one of them, and a product label is on the bottom of the other one.

They are very compact, but there is a lot of stuff in there.

The rear panel has the port, but also, a pair of RCA analog inputs for an MM phono input along with a grounding lug, an optical input, a 1/8th-inch stereo plug input, an HDMI eARC input, and a LAN connection. The AC socket is on the bottom left.

Setting up the BluOS connection between the M66 and Alpha iQ speakers is straightforward. First, you’ll need to download the BluOS app onto your Android or Apple phone. If you have a single Wired or Wi-Fi network in your home, once BluOs is logged into it, it will automatically discover any other BluOS-enabled devices on that network and allow you to select them for set up and use. I have two WI-Fi networks in my home, so I had to manually set a “reservation” for the NAD’s IP address to make sure it logged on to the correct network. The speakers have an IP address too. Here are two links to important resources on setting up BluOS with the NAD M66 and PSB Alpha iQ speakers:

Connecting Alpha iQ speakers to your network
https://support.psbspeakers.com/hc/en-us/articles/7708839858967-How-do-I-connect-Alpha-iQ-Series-BluOS-Enabled-PSB-Speakers-to-the-network

Factory Reset (do this only if required during setup)
https://support.psbspeakers.com/hc/en-us/articles/7809232688535-How-do-I-perform-a-factory-reset-on-my-iQ-Series-Speakers#:~:text=Disconnect%20the%20secondary%20Speaker%20from,SERVICE%20button%20for%2030%20seconds.

Here are some screenshots from my Android Phone during the setup procedure and use. BluOS supports Qobuz and Tidal (among many other streaming and internet radio services) from within the app itself. I was using my Qobuz subscription through BluOS without issue.

The sound with BluOS through both the M66 Streaming Preamplifier and Alpha iQ Speakers was excellent. The speakers in particular sounded open and clear, if just a touch thin in the midrange. Bass was nice for such a small driver, but, of course, there is only so much a 4” woofer can do. In a small office, dorm, or bedroom, I could see these as being an ideal solution. For a larger space, a subwoofer in the 10” range would be a good addition to this particular set of speakers. Occasionally I felt that the top end sounded slightly edgy, but I am really tuned in to that (the tweeter is a metal dome – I like silk dome tweeters, just my personal preference). There was no unusual tonality to anything, including piano, violin, or human voices. Instruments and vocals sounded very much as they should. The bass was not boomy either.

I also tried the M66 as a streaming preamp in my main system. Using my phone via the BluOS app, I directed the M66 to stream music directly from my Qobuz account. The NAD Masters M66 preamp sounded positively world-class. The power amplifiers I was using were Pass Labs X600.8, and the speakers were the Sonus faber Lilium. The very low distortion from the M66 (see the Bench Test section) made for clarity and transparency that many of us would find incredibly satisfying. For those who prefer more warmth rather than what some might call a “dry” sound of extremely low distortion, pairing the M66 with a tube power amplifier would be spectacular.

Here are my opinions on the M66 with the X600.8s and Liliums:

The NAD M66, when paired with Art Pepper’s fluid, expressive saxophone work, didn’t just play music – it painted a scene.

From the first breathy note of his sax, the M66 revealed its talent for nuance. Pepper’s delicate phrasing, the way air vibrates through the reed before the full-bodied tone blooms—it was all there, untouched, uncolored, simply alive. Credit the low distortion of this preamp that allows every subtle inflection, every whispered moment of improvisation, to shine through.

Then came the rhythm section – the upright bass impact, the drums snapping with a crisp authority, the piano’s chords resonating with a fullness that felt tangible. The M66 captured not only the notes but the space around them, making the room feel like a smoky jazz club from decades past.

What impressed me most was the preamplifier’s ability to handle dynamics. When Art Pepper soared into high-register flurries, the M66 stayed composed, never shrill, never brittle – just pure, controlled energy. And when he leaned into a bluesy ballad, the warmth of his tone wrapped around me, intimate and unfiltered.

This wasn’t just playback; it was presence. And that, to me, is what makes a preamplifier truly great.

Listening to Fanfare for the Common Man through the NAD M66 was nothing short of a revelation—a towering, cinematic experience that shook the air with the weight of brass and the thunder of percussion.

From the first strike of the bass drum, the impact wasn’t just heard; it was felt, resonating in the chest. Each drumbeat rolled through the room with an authority that was powerful yet controlled, never bloated, never overbearing – just pure, unshakable force. The decay lingered in space, stretching into silence with a natural, organic fade, allowing the music’s grand architecture to breathe.

Then came the trumpets – bold, gleaming, and searingly brilliant. The preamplifier rendered them with razor-sharp clarity, yet without a hint of harshness. The upper registers soared effortlessly. Every articulation, every crescendo, was delivered with a sense of immediacy.

The sheer scale of sound really impressed me, but also it was the space between the notes. The M66 accurately relayed the vastness of Copland’s vision, placing instruments in a stage so convincingly wide and deep that it felt as if the walls had dissolved. The timpani rumbled in the distance, the brass played with unwavering confidence, and the final, resounding strike of percussion left an imprint that lingered in the silence.

Listening to Kind of Blue through the NAD M66 was like stepping into some imaginary smoky, dimly lit studio where Miles Davis and his legendary quintet could have laid down these immortal tracks.

The moment the first muted trumpet phrase of “So What” floated through the speakers, the M66 made its presence known – not by imposing itself, but by disappearing entirely. Miles’ tone was hauntingly intimate, the bite of his Harmon mute perfectly captured, neither too sharp nor too veiled.

Then came Coltrane and Adderley, weaving saxophone lines with effortless grace. The M66 relayed them with such clarity that their contrasting styles became even more vivid—Coltrane’s searching, angular phrasing cutting through with precision, while Cannonball’s alto sang with velvety warmth. The interplay between them was electric.

The rhythm section – Evans’ gentle, impressionistic piano voicings, Chambers’ rich bass foundation, Cobb’s whispering ride cymbal—was where the M66 truly shined. The bass wasn’t just deep; it was alive, resonating with a woody, tactile presence that anchored the entire performance. The cymbals, instead of being washed out, had a shimmering, airy quality.

But the real magic? The silence. The NAD M66 didn’t just reproduce Kind of Blue—it respected it. The quiet moments, the spaces between the notes, the anticipation before the next phrase—those were just as profound as the music itself.

Some components reproduce music, and then others seem to unfold it, layer by layer, note by note. The NAD M66 belongs to the latter category. Listening to Luis Fernando Pérez’s Rachmaninoff – oeuvres pour piano album through this preamplifier was less like pressing play and more like opening a door into an intimate concert hall.

From the very first notes, the NAD M66 proved itself a maestro of warmth and detail. The rich harmonics of Pérez’s touch – so essential to capturing Rachmaninoff’s melancholic grandeur – were rendered with astonishing depth. Each keystroke carried weight, not in the sense of heaviness, but in its fully realized presence. The decay lingered just long enough, the hammers striking the strings with a tactile realism that made me forget I wasn’t in the same room as the piano itself.

It wasn’t just the piano’s body that impressed me—it was the air around it. This preamplifier breathes. The space between notes was alive, the subtle pedal work whispering through the background with a natural, organic presence. The treble extension was pristine but never sterile, allowing the singing, bell-like qualities of Pérez’s phrasing to shine without harshness. Meanwhile, the midrange was lush, velvety, and emotionally immediate.

And then there was the bass and the NAD M66 rendered it with honesty. The weighty left-hand chords didn’t just hit—they resonated, enveloping the room in a warm, golden glow. It was the kind of bass that doesn’t just support the music but elevates it, grounding it in something deeply physical yet never overbearing.

Whether whispering through the introspective moments or roaring with Romantic grandeur, this preamplifier delivered with an effortless musicality that felt less like a piece of equipment and more like an extension of the recording itself. With Pérez’s sensitive interpretation and the NAD M66’s ability to capture every nuance, I wasn’t just hearing Rachmaninoff—I was feeling it.

Norah Jones’ Come Away with Me through the NAD M66 felt like an invitation – an intimate performance, as if Norah Jones had set up her piano in a candlelit room, just for me.

From the very first notes of Don’t Know Why, the was an effortless warmth, a sense of space so natural that the music didn’t just play – it breathed. Norah’s voice, delicate yet full of quiet strength, floated through the air with stunning realism. The M66 captured every subtle nuance – the gentle breaks in her phrasing, the whispered vibrato, the way each lyric seemed to hover, suspended in time.

Then came the piano, rich and resonant, its notes falling like raindrops on still water. The preamplifier handled the delicate balance beautifully – never overwhelming, never thin – just perfectly weighted. The upright bass, warm and round, provided the heartbeat, each pluck rendered with a deep, organic presence that felt almost tangible.

The M66 unraveled her guitar strings with finesse, allowing the soft, fingerpicked lines to shimmer. The subtle brushwork on the drums was given space to breathe, the cymbals whispering with a crisp, airy sweetness that never intruded, only enhanced.

Through the NAD M66, Norah’s album wasn’t just heard – it was felt, like a gentle hand reaching through the years to remind you that some music, and some moments, are timeless.

The human voice is the most delicate and powerful instrument, and here, listening to the Sacred Treasures of Venice, it was rendered with breathtaking purity. Each choral line emerged not as mere sound, but as an ethereal presence, floating effortlessly in a vast expanse of air. The M66 did not simply present voices – it unveiled them.

The bass voices, deep and resonant, anchored the entire space, their warmth enveloping the listener in a foundation as steady as stone. The altos and tenors wove together like threads in a tapestry, their harmonies having an almost tangible depth. And the sopranos – clear, soaring, angelic – never piercing, suspended in the air as if untouched by gravity.

The M66 handled the reverberation with stunning grace, capturing the natural acoustics of the recording’s sacred space without a hint of muddiness. The echoes did not blur the articulation but rather extended it, stretching each note like ripples on water, allowing the listener to feel the grand scale of the venue itself.

Next up was Camille Saint-Saëns’ Cello Concerto No. 1, performed by the masterful Bruno Philippe.

From the first impassioned sweep of the bow, the M66 captured the cello’s full-bodied resonance with stunning realism. The instrument did not simply “sound good” – it existed, tangible and alive, vibrating with every breath of Philippe’s phrasing. The lowest notes, rich and sonorous, emerged with a weight that was not bloated but deeply grounded.

Then there was the orchestra – a delicate yet powerful counterpart. The strings shimmered, the winds whispered with expressive clarity, and the brass surged forth in moments of grandeur without ever overpowering. Every section of the orchestra was placed in perfect harmony, never vying for dominance, each voice given space to shine.

The dynamics were intoxicating. When Philippe’s bow danced lightly over the strings, the M66 translated every nuance, every featherlight touch, with an intimacy that felt as if the listener had been granted a front-row seat to something profoundly personal. And in the fiery passages, where the cello soared with dramatic intensity, the preamplifier responded with effortless control—never compressed, never strained, only pure emotion.

This was not just a performance – it was storytelling in its purest form. And the NAD M66? It was the silent architect behind it all, ensuring that every note, every dynamic shift was heard exactly as it was meant to be: with soul, precision, and an overwhelming sense of presence.

The NAD M66 preamplifier delivers music with effortless clarity and warmth, and there’s no better way to test its finesse than with Tony Bennett’s Perfectly Frank. This album, a heartfelt tribute to Sinatra, is all about smooth vocals, lush orchestration, and intimate storytelling – and the M66 brings it all to life with stunning realism.

From the opening track, Bennett’s voice is front and center, rich and expressive without a hint of artificial enhancement. The M66 lets every nuance of his phrasing shine – whether it’s the slight breath before a lyric or the natural warmth in his lower register. There’s a smoothness here that makes listening easy and immersive, with none of the harshness or compression that can sometimes dull the charm of classic recordings.

The orchestral backing is just as impressive. The strings glide effortlessly, the piano chords have just the right amount of weight, and the brushed drums maintain a soft, natural presence. The M66 ensures that every instrument has its place, never overpowering Bennett’s vocals but always supporting them with the right balance of detail and space.

What stands out most is how natural everything sounds. There’s no artificial boost to the bass, no exaggerated treble—just a clean, well-rounded presentation that makes it feel like Bennett is singing right in the room. The soundstage is wide but not exaggerated, keeping the performance intimate while still giving each instrument room to breathe.

If you’re looking for a preamplifier that delivers music with warmth, depth, and an effortless sense of realism, the NAD M66 is an excellent choice.

For the bench tests, I used the XLR Analog Inputs, both in direct mode (bypasses the ADC and DSP), non-direct mode (goes through the ADC and employs DSP), and the XLR AES/EBU digital input. The results of all three variations are included in the graphs shown below.

First, the XLR analog inputs are in direct mode.

1 kHz with 1 Volt in and the volume control set to 98. Output was 1.084 Volts. Distortion is almost at the low limits of my Audio Precision Spectrum Analyzer.

The same test with 4 Volts input and 4.335 Volts output (Figure 2) yielded less distortion in terms of THD+N, but there are actually more harmonic peaks. The resulting overall lower THD+N is due to distortion not increasing in the same relative amount as the increased fundamental sine wave peak. That is why it is necessary to see the spectrum instead of just looking at the numbers.

The standard IMD test of 60 Hz and 7 kHz also resulted in very low distortion at both 1 Volt input (Figure 3) and 4 Volts input (Figure 4). These are distortion levels I have seen in only a few preamplifiers.

With 19 kHz and 20 kHz test sine waves, again, very very low distortion. Whatever additional side peaks there may be in the higher voltage output (Figure 6) are buried in the higher noise floor. One difference though is the visible 1 kHz B-A peak with the high voltage input. Using 4 Volts in and out is just for testing purposes. If you did that with your power amplifier and speakers in the path, they would go into a space orbit along with your windows.

The Frequency Response is shown in Figure 7, below, at different voltages, and with expanded scales in Figures 8 and 9. You can see that the response is pretty much ruler-flat between 20 Hz and 20 kHz, and then a very small attenuation (0.1 dB) between 50 kHz and 150 kHz.

THD+N vs. Frequency is also very special (Figure 10). It is 0.001% or below at all frequencies. At 4 Volts, there is a rise in distortion out between 2 kHz and 30 kHz, but it does not go above 0.001%. This is some preamplifier.

THD+N vs. Output Voltage is shown in Figure 11 and 12. In Figure 11, the load was 100 kOhms. The knee is at 3.5 Volts, but output at 12 Volts still has low distortion. That is pretty much the maximum usable output since distortion rises quickly to clipping beyond that point.

In Figure 12, below, output into 100 kOhms and 600 Ohms are shown together. They are pretty much the same, which is excellent. It means the M66 has one heck of a power supply.

Now, we move on to the XLR analog input, but not in direct mode, so the signal passes through an ADC so that DSP can be applied.

At 1 kHz, 1 Volt in, 1.1 Volts out (Figure 13), the distortion number is low, but there are more harmonic peaks than in the direct mode (Figure 1).

At 4 Volts in 2.5 Volts Out (Figure 14), clipping occurred. Even with only 320 mV out (Figure 15), clipping still occurred. So, it appears, the ADC is limited as to its input analog voltage.

Moving back down to 1 Volt input and 2.77 Volts output (Volume set to 100), the signal is fine (Figure 16).

Using 2 Volts input also resulted in clipping at 1.1 Volts output (Figure 17) and 98 mV output (Figure 18). My suggestion for using the XLR analog inputs is to set it in Direct Mode so as to bypass the ADC since it is voltage input limited. Some CD players have 3-4 Volts output would cause clipping if the XLR inputs are set to the Non-direct Mode.

IMD with 1 Volt In was a very low 0.0008% (Figure 19).

19 kHz, 20 kHz side-peaks with 1 Volt in (Figure 20) were also very very low in number and height.

THD+N vs. Frequency (Figure 21) had more distortion than in the direct mode (Figure 10)

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And, THD+N vs. Voltage Output showed that, with the ADC in the circuit, there is less output capability with a 600 Ohms load (Figure 22). This is not important since most power amplifier input impedances are 50 kOhms and above. The point is, though, that there is a difference.

Here are the bench test results using the AES/EBU (XLR) digital input;

1 kHz, 16/44.1, 0.001 dBFS input, 2.14 Volts output (Figure 23). THD+N was 0.003%, which is a bit higher than with the XLR analog direct (Figure 1). This is expected because the signal has to pass through a DAC. Still, the distortion was very low.

Distortion was the same (Figure 24) with 5.38 Volts output (increasing the volume).

With 24/192 sampling (Figure 25 and 26), distortion was slightly higher than with 16/44.1 sampling. Notice how low the noise floor is.

For the IMD tests (Figures 27 – 30), distortion was lower with 24/192 sampling than 16/44.1 sampling, the opposite of the 1 kHz tests.

19 kHz and 20 kHz test spectra are shown in Figures 31 – 34. The side peaks are very low in number and height. Excellent results.

Frequency Response is shown for 16/44.1 sampling (Figure 35), 24/96 sampling (Figure 36), and 24/192 sampling (Figure 37) at several different voltages. The low-pass roll-off is very fast (sharp). See The Mathematics of How Analog-to-Digital (ADC) and Digital-to-Analog (DAC) Converters do Their Job for a complete description of how low-pass filters work.

THD+N vs, Frequency is shown in Figure 38 below. There is more distortion in the 16/44.1 high frequencies than in the 24/96 high frequencies.

I tested the M66’s ability to reject jitter. In Figure 39 below, I inserted 531 pico-seconds of 1 kHz sine jitter into a 10 kHz sine wave signal. If the M66 DAC had passed that through, there would have been a large peak at 9 kHz and 11 kHz. As you can see, there are no peaks, which means that the M66’s DAC has a re-clocking circuit.

Figure 40 shows the same jitter test at 24/192 sampling. There are no jitter peaks at 9 kHz or 11 kHz. There are some small -115 dBV peaks at 19 kHz and 20 kHz. They are also just barely visible in the 16/44.1 jitter test (Figure 39). These are artifacts, not something due to the jitter.

Using BluOS with either the PSB Alpha iQ speakers or the NAD Masters M66 Streaming Preamp allows easy high-res audio streaming from any of several integrated streaming sources directly to either component. As it stands, the BluOS platform is the only real direct competitor to something like ROON. There are differences and it isn’t as brand agnostic as ROON is, but BluOS is free when you purchase compatible hardware, and it integrates with far more streaming services and online music sources.

Speaking of hardware, I found the NAD Masters M66 Streaming Preamplifier to be a world-class analog preamp that has extensive digital resources and “Swiss Army Knife” flexibility in the bargain.

The PSB Alpha iQ BluOs Streaming speakers are a fun and great-sounding turnkey streaming solution for small to moderate spaces. Both are great examples, at different ends of the spectrum, of what the BluOS platform can do.

Look for more specific and focused reviews on each of these products coming soon.