I've heard Mac 402, 501 on Zu Definitions in my own system, and 252, 402, 501, 1201 on a system I am familiar with using Sonus Faber Cremonas. I've also heard the MA6900 integrated on both, as well as on a system with Sonus Faber Cremona Auditors.
Preamps used have been C46, Audion Premier 1.0, Django TVC, Klimo Merlino Gold, Audiopax Model 5.
The Mac quad-differential amps are unfailingly musical, rich in satisfying, realistic tone, very wideband and dynamically convincing. All this is a real turnaround from Mac solid state amps from the first through about 1990, when Mac solid state amps sounded smooth but dark and uninspiring. Quite antiseptic and atonal. The designs produced from around 1990 through 1996 or 98 were transitional in moving toward the sound McIntosh has achieved today, but still held back by the old sonics, to some degree.
Today, even the non-autoformer amps, like the 6300 and 6500 integrateds sound good, but the autoformer amps are the ticket to tone, with the quad-differential or double-balanced amps performing at a premium above that.
I own single-ended tube amps, dynamic and musical, and my 101db/w/m speakers don't really demand more than what I have in dynamic power. But more couldn't hurt if clarity and tone doesn't suffer, right? If I invest more in amplification than what I have, MC1201 monoblocks would be serious contenders. A 402 puts you just within the same family sound.
One thing these Mac amps have is the muscle and control to get an unruly speaker talking in one voice. The bigger the better -- you will hear better driver integration and if you go high enough in the line, crossover effects will begin to be mitigated. There are just a handful of transistor amps I'd consider listening to today -- McIntosh autoformer units, Pass and First Watt, Lavardin and maybe Channel Island -- and MC402 and above are front and center. I am certain you will hear a compelling difference between even an MC252 over a 2200/2205, but the step from there to a 352 or 402 is easily discerned as being worth the improvement in tone, expression and dynamic realism.
Phil