I had the MC252 and now have a pair of MC501's. My speakers are Sonus Faber Cremona 3 way floor standing speakers which are very efficient, 91 db at 1 watt. The first thing I noticed even before the 501's were broken in was that the sound stage had more 3 dimensional separation and much more bass. Where the MC252 had terrific center imaging for vocals it did not erase the fact that I was listening to sound coming from a speaker. With the 501's I could look straight at the speakers and yet the sound seemed like the music was coming from everwhere but the box, a very freaky feeling. When listening to music with wide swings in dynamic range, Flim and B B's for example the sudden bursts are effortless for the 501's. With more complex classical or rock music the 501's display a musical canvas where every instrument and vocal has its point on the sound stage. I can't imagine getting rid of mine for a very long time. You can buy MC501's on the used market for $1000 more than the MC402 all day and be able to resell them for what you paid. While the MC402 are a nice amp. to me they sound more like the MC252 then the MC501's.
Best Amp for McIntosh sys.- MC252, MC402, or MC501
I am upgrading a system that I have for about 40 yrs. Recently purchased a MCD301 sacd/cd player, MR85 tuner, and Paradigm Studio 100 series IV speakers. Still have C26 pre-amp and MC2505 amp (both recently serviced by MAC). I am happy with the sound but am afraid the days of shipping the amp back and forth for service are limited. The spks are rated "Suitable amp power range 15-350 watts" and "Amplifiers that exceed-power range are recommended". I don't intend to make another amp upgrade and am leaning toward the 501.