I'm no good at this sort of thing. It sounds like clipping There is a decrease in clairity, an increase in perceived loudness and high frequency content. Maybe one of our more right-brain active types can do better?

In any case, it's unlikely you really need 200 watts on all channels - a pair of m200s or a good stereo power amp in front would probably do it if you do in fact need more power. You can actually get some really good amps on eBay if you know what to look for. I'm particularly fond of the older Hafler amps. I bought a mintish XL-280 a few months back for about $240, including the shipping.

Using an amp for the fronts also should free up some extra ooomph for the other channels.