Polk RM 6880

[The Black Pearl]

I am thinking about buying the above. Without breaking the bank what would be a good speaker to add to this 5.1 system. My new amp is 7.1 and I was thinking of using the 6880 speakers for the rear and possibly the M10 for the front. Considering I am using 6.1 Logitech speakers through a sound blaster extigy that I put together over 4-5 years ago, 6.1 surround was not available for home. I was on a budget, won speakers at a golf game and bought the card refurbished for $90. Works well, but the girls do not know how to get the speakers to work via the logitech harmony, the existing system just does not sync well with the TV.

Thanks