I have the M2-1500M (a pair of course) and it sounds awesome. I wouldn't worry too much. I'm pretty sure there are subtle changes between M2 and M3, maybe in the buffer stage? Just guessing. I've heard a lot of amps in all classes that I know of (A, AB, C, D, T) and to me the M2 is definitely one of the best I've heard. In it's price range it's no doubt the best.