When speaking of power, I mean simultaneous power. Most recievers cannot meet their rated output with all channels driven at once ( a quick look at the specs will reveal that the rated power is usually with two channels driven). With seperates each channel or pair of channels can have its own power supply and all channels can be powered equally. The surpluss of available power means that the system is not working hard, and should sound better.
The problem is that there is very little source material that requires full power from all channels at the same time for any extended period of time. Basically for most normal listening at reasonably sane volumes with reasonably efficient speakers a standard reciever should fit the bill just fine.