Audio Research versus McIntosh tube amps: anyone experience or compare both?

I at one point I had both a Ref 75SE and Pass xa25 in my system. I concur with @chcook's statement " I actually find the XA to have more midrange warmth than the Ref 75. I really like them both a lot - Ref 75 edges out the Pass on soundstage, and Pass seems just a bit warmer/fuller in the midrange." I will add that I thought the Ref75SE had a little blacker background.

Let me add this: my system photos feature a few of an ARC amplifier - a vintage VT100 purchased from a friend last year.  It’s been hot rodded with new caps plus kt 120’s and sounds very good in my set up - better than I had expected!  But it has two issues: a fan which I dislike ( audible) and it’s a PIA to bias (never mind the cost of replacing 16 tubes …).  Hence my thinking a more modern, easier to deal with tubed unit might do the trick.

Anything preowned would of necessity be bought without an audition in my set up and thus it’s a bit of a guessing game.

Other suggestions welcome and thank you!

Pick up an ARC D-79A or D-79B.  Even used, a lot of people think it was the very best amp ARC ever produced.  

"Pick up" was used figuratively.   

I have an audiophile friend who switched from pass lab XA160.8 to ARC ref250. Paired with ARC ref10 pre amp he and I just love how they sound with Magico S3. If you like details and “fast” response with a little tube bloom then ARC is one of the very few maker who can make this balance meticulously. Macintosh IMHO is more “classic” tube sound : “musical” (=slow transient response so not too much details ) but each to their own. 
disclaimer : current user ( and big fan）of ARC ref10 / ref 160 mono mk2 , I had used CJ / Counterpoint / Jadis / Mac / Kondo / Manley in the last 25 years and these are the best tube pairs I had ever used. 

Maybe try an ARC VS110 or VS115. Not an ARC reference level amp, but might have that warmth you are looking for while still retaining that ARC sound. Uses 8 6550 tubes and easy to bias. I also agree with the Ayre recommendation. I moved from the VS110 to a Theta Dreadnaught II (which like Ayre is a zero feedback Charlie Hansen design) and the bass drive is fantastic with very detailed mids. The Theta also has 225 watts/450 watts into 8/4 ohms vs the ARC rated at 110 watts. Both the VS110 and the Theta are available for around $2,500.