Audio Research is a pre-eminent manufacturer of CD players, preamplifiers, power amplifiers, and DACs. All use tubes except for the CD player.
The LS28 Line Stage Preamplifier is one in their Foundation Series. At $7,500, it is not cheap, but it is less expensive than the REF 6 ($14,000). The difference is that the LS28 uses four 6H30P dual triodes, while the REF 6 uses six. The LS28 has a solid-state power supply, and the REF 6 has a tube-based power supply.
The LS28 is capable of 17 Volts output, but you only need about 2 Volts. This means the LS28 just coasts along with no strain.
The 6H30P tubes are dual triodes with a very low impedance which means it can drive just about any input. They are configured as fully-balanced, so you have a choice of a single-ended or balanced signal path.
You are in for a treat with the full review, coming shortly. The LS28 sounds terrific, and I am not surprised, as Audio Research products are all excellent.