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

Most definitely the ARC, but you were on the right track with the XA25... Why is the obvious answer a tube amp? 
A really good option, and one I ran with big B&W's... ARC Pre, big Pass amp! I used an X250.5 at the time, but if you want tube like sound as opposed to intense focused bass, crystal clear mid & hi's.... Big mono XA's!
XA60.8's will sound completely different than your XA25
$14K a pair new... there are 3 year 0% interest deals out there...

I bought an Arc REF75 so long ago I cannot remember, sent it to ARC and had it upgraded to REF75se another long time ago.  I have never had the thought to ever change amps, I am pretty sure this is endgame for me.  A year ago it started sounding muddy in the bass and lost detail, checked the hours, 2030 on those power tubes.  Put in new tubes (from ARC, yeah, reluctantly paid the price) sounded much better immediately, now 80 hours in it sounds wonderful again and I know it is just starting to bloom, in another 200 hours, back to audio bliss.  Pairs perfectly with my ARC REF6.  After reading reviews and talking to people I am feeling I will prefer the REF6 sound to the REEF6se sound though that is a somewhat baseless opinion because i have not been able to spend some time with the 6se.

Bottom line: another vote for the REF75se.  Not the ref75.  Big difference!   I listened to MacIntosh years ago.  I found the Macintosh to be a fun listen now and then, but too bloated and exaggeratedly tubey.   I wanted some thing more natural, like the musician was in the room with me, with a hint of warmth. My cables amplify the tiny bit of warmth I hear in the ARC. 

I would also suggest if you could afford it, eventually maybe, pair it with the REF6 Pre, to me it sounds like they were made for one another.  I added the REF6 after I had had the REF75 for awhile, and that changed everything - I could no longer listen to how my system was sounding because the music kept distracting me.  Except for adding a server (Aurender) I haven't changed anything in a long time.

Spending money on Head-Fi now.

Some of the statements about the sound of each amp mentioned above my post are generally true.  This is the best advice I have read.  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.  BUT you have to have them modified.  We recently upgraded a D-79B and were amazed at how it sounded once upgraded.  BUT it is a big beast! LOL.

I don't see your source so I am thinking you are getting your sound quality from the source and not as much from the amps but I am not there to help you evaluate that part of your sound.

Happy Listening.

@vinocour

Very nice account of your experience with ARC. Very similar to mine although I have spent the last few years with the Ref 160s and 160m.

Judging by your comments on your main system I must highly recommend the Woo WA5 headphone amp. If you can afford it add a pair of Takatsuki 300B tubes and you will be in the the same headphone nirvana which all ARC does to your main system,

I've moved on from ARC gear. Ime it sounds superficially impressive, plenty bass, dynamics, big soundstage but lacks musicality when compared to the best. I'd be happy to have it in an AV system. Macintosh are midfi at best and don't belong in a reference system.

An earlier poster suggested mixing a valve pre amp with solid state power amp. For me this is audio nirvana, i would suggest a VAC pre with a Boulder power amp.

This would give the warmth you enjoy and the bass you crave, with added musicality. A mailed fist inside a velvet glove.