Kind of fun to see a year and a half old thread come back to life. It is still relevant.
I went through a period of time searching for the right amplifiers to drive my Sonus faber Amati Anniversario speakers. I started with a single MC275 MkV, then purchased a second one and operated them in parallel mono configuration. The amplifiers are quite good but have a bit of a loose bottom in the lowest octave when pushed to deliver power. I replaced the pair of MC275's with a pair of MC601's. Night and day difference in the presentation. The lowest octave firmed up and became richly textured and the dynamics improved with the additional power on tap. Then I purchased the MC452 power amp. Doing A/B testing against the MC601's I discovered there was very little difference in the performance or voicing. They are first cousins. Then I sold a pair of MC601's and purchased a pair of MC2301 tube power amps. I had four MC601's at one point and still have two in the living room system. The MC2301's absolutely mesmerized me with the Anniversario's. The lowest octaves remained soild and robust, the midrange liquidity left me slack jawed in amazement and the upper octaves were pure bliss with lots of air around all instruments and voices. Additionally, the MC2301's were dead silent with a wonderful velvet black background. These are the amplifiers still in service driving my Anniversario speakers. Truly astonishing performers.
Since I had the opportunity to make direct comparisons using my C1000C/P preamp with the MC275's, MC452, MC601, and MC2301 power amps, plus an MC352 I had at the same time, I have a relatively clear perspective on how all of these very fine power amplifiers perform. It is no mistake that the amplifiers I still own and use are the MC2301's, MC601's, and the MC452. In my opinion these three amps are the cream of the current McIntosh lineup. I consider these three amplifier designs to be the best McIntosh has ever produced. There is no way to go wrong with any of them.