I've read here and elsewhere anecdotal accounts of the smaller amp's superiority. I'm sure you've read them too. Expectation bias?
That being said, I'm willing to entertain the possibility of real differences before writing off the experiences of others. If there are differences as reported, they should be identifiable, reducible differences that can be measured. Here are my thoughts, having only possessed the C372 myself. The pre-amp stages are pretty much identical between the two amps in question. The smaller amp might rely on the gain from the pre stage more than the big amp, which could result in measurably superior s/n on what's fed to the amp section. Op amp output stages typically have better specs with greater output. Now, I've never known anyone to put this to the test, but it could account for some folks preference for the smaller amp.
edit: Input sensitivity for the smaller amp is specified at 630 mv. The big amp's data sheet does not provide that information at all. Previous iteration C372 input sensitivity is 770 mv. I think that makes it backwards from my theory, but it would make the smaller amp louder at the same input, and we know that louder is preferred, even very slight differences.