This is what I was told by a dealer concerning the Classe CA-2200 stereo amp versus the CA-3200 three channel amplifier using only two of the channels. He said that the CA-3200 sounded better because of the bigger power supply in it. I never actually sat down and compared the two, but what the dealer said sounded logical.
One of the first things that is addressed in an upgrade is beefing up the power supply. So, given that if the two Rotel amps are identical in quality, if the multichannel amp has a larger power supply, it might be better.
Chuck