Bob045,
It seems to me like the M200 would be a perfect match for your speakers power-wise that is. 200W amp and 200W rating on the speakers. No reason to fear for the life of your speakers. It's been my experience that most speaker damage is done by overdriving an underpowered amplifier. Those poor little tweeters just don't take too kindly to an amplifier that's driven into clipping.

As to the issue of relative channel balance, that's a matter of speaker sensitivity and amplifier gain, not it's ultimate power rating. The mains may ultimately be able to play louder when the system is turned up because of the extra power in reserve but you don't want to go past the point where the other channels start to give up the ghost anyway. Your speakers are rated at a middle of the road 90dB so I don't think getting the loudness levels in line with the center and surrounds would be an issue. I assume the Yamaha has facilities for channel balance calibration.

------------------
Tekdredger