Surround Sound Systems

Surround Sound Systems: 5.1 or 7.1?

I'm going to be in the market for my first surround sound system. I was wondering if you know if what I'm looking for exists. I'm looking for a surround sound system that can be expanded to more speakers. Like a system that is a 5.1 surround that has ports to add an additional two speakers to make it a 7.1 surround. A kind of modular surround sound system. I'd love to get the 7.1 right away but if I can save some money right away with a 5.1 and maybe in 6 months or so add a couple speakers that would be the best.

- Bill Russell
Bismarck, ND