I've heard the 402 a bunch and listened to the MA7000 a few weeks ago for a long time. I haven't heard the 6600 yet but the MA7000 is the one to compare a 402+Cxx to anyway. All I can say is the 7000 was really a special amp. I heard it on Avalons and DALIs and both were fantastic (G08 source). Beautiful, organic, natural, and yet highly detailed and dynamic at the same time. Quite a feat. We pitted it up against top-level Accuphase and there was no comparison - the McIntosh had so much more presence and emotion, it was amazing. The 7000 is a big step up from the 6900 in every way. The only advantage the 6600 might have over the 7000 is the digitally-controlled volume.
Arthur
Arthur