You could be right about the Yamaha's, but wait, they dropped a lot in ACD tests but those were when "continuously driven". S&V did not do such tests for short term driven conditions. So we really do not know how Yamaha receivers would perform in ACD when amplifying music or movie programs.
For those who use 7 channel stereo a lot, that could become a valid factor, but in practice, unless one listens to higher than average spl in a larger room, even if the ACD output drops from 140W to 50W, the amps would still be well below their clipping point. That is because with all 7 speakers going, you get a few dB boost in spl from your listening positions, and that could be equivalent to having the higher 2Ch power rating back. For party music, it will likely have very little dynamic peaks so then again, 50WX7 simultaneously will most likely be more than enough. Also, even the Emotiva 5 channel 120W amp won't sustain 600W total continuously anyway. Except for amps that are designed for it, the so called "continuous" rating does not imply literally continuous, it is just for long enough duration that can take care of real world music/movie programs without overheating the amp.
All in all, really a moot point. I would take a Yamaha AVR that has superior dynamic output over one (even separates) that offer 2ch output slightly higher than their ACD output, just as an extreme example.
