Before buying the M3, I compared it with the top end Marantz and I thought the M3 didn't sound like it was "struggling" to drive a pair of Totem Fire monitors. The Marantz seemed to be "running out of gas", especially listening to dynamic symphonic music.
I always wanted McIntosh equipment, but before upgrading from the M3, I told my wife that I suspected it would sound "different", but not necessarily "better"...boy was I wrong. The McIntosh just sounded smoother, more "musical", didn't seem to have "its sound".
The MA660/6700 both have the McIntosh "autoformer", which I suspect has some role in the smoothness of its sound.
I've since upgraded to McIntosh separates. One distinct advantage in McIntosh equipment is its ability to hang on to its resale value.