Doozy of an amp question

I can’t answer your question directly and admittedly have not heard the Macintosh amp. I have heard  the simaudio. I’ve also owned a couple of  SimAudio products and I found them to be very well built, reliable, and competent.

I can appreciate the difficulty you have with in-home auditions. Even if you can’t do that, I suggest you try to listen to these components at a dealer location because I think the McIntosh house sound and the sim  house sound are quite different. it seems likely if you like one, you may not favor the other. The Macintosh amps I have heard tend to be sweet, critics would say dark and veiled, proponents would say musical. The simaudio Amp is more detailed and transparent, critics would say dry and analytical although that would not be my view, I think it delivers to the speaker the signal it receives without coloring it inany way, not a bad attribute for an amp. Although it’s always better to listen in your own set up, I think if you could hear these two components at dealer locations, you could at least get a good read on which House sound you like because they are very different.
good luck!

I would look for an ARC amp to match the preamp you own

There's no way of knowing in advance how two components will align with each other. Actually, three components, the speakers, power amp, and preamp. I'm not an ARC guy, but I agree with jperry's comments that ARC is the safe choice. Anything else, the results could be anything, and odds for a mismatch are good.

I agree with jperry and lynn_olson. Nothing will match with your ARC preamp like an ARC amp.

There are so many BP much better then that Mc parts quality leaves a lot to be desired, I owned a audio store for years belong to many audio clubs 

what are you speakers is the 1st question how big is your room ,how loud  do you want to play it ,your speakers and their efficiency first and foremost.

the Coda 50wpc 5.5 pure class A for $6500 a Great Amplifier to start this , Coda has excellent class AB amps that have 3 power  to choose from up to 18 wpc to start into pure class A bias , what’s your budget too , Pass Labs 

some very good classD  amps using Gan Fet technologies  I have the Latest 

Very high current monoblocks  from classD audio .com  excellent and would never know what it is it judt get out of the way of the music ,and power to spare. And under $2500;can  competes with much more expensive amps. Lots of good amps out there to choose from.