I use NAD C372 with MA RS6. They work extremely well together. The NAD is pretty powerful, warm and rounded, while the MA RS6 towers are entertaining and forward sounding. A perfect match.
I also have a CA 640 amp. You cannot compare it with NAD C372 (or C272, which has the same power-amp). The NAD is significantly better, but it is twice as expensive too!
MA RS6 deserve a powerful and warm amp. This package might bust the budget for someone who started with BR5. That is why I suggested BR5 for MPW. Unlike RS6, the BR5 have a warmer and more laid back sound. They will work well with cheaper electronics.
BTW, I would recommend MA BR5 and RS6 over their respective bigger brothers the BR6 and RS8. The bigger speakers have an extra woofer, added as an after thought. This extra woofer makes the BR6/RS8 sound more impressive during a 5 minute demo, but spoils the frequency balance to a great extent.
Thanks,
Sharad