Can I Pair Audio Reseach Ref 3 w/ the McIntosh MC2505 Poweramp?

Sorry, IMHO the 2505 is not one of Mac's better efforts.  Matching a high end pre will not make the Mac 2505 any better, but only highlight it's shortcomings. You may taking a big step backwards.

You don't have your system posted or say what kind of sources you prefer to use, so it's difficult to give precise input.  If you're a vinyl junkie with a hot table, arm and cartridge, that's one thing.  If you're all-digital and into streaming, that can often be something else.  Much (if not all) also very much depends on your speakers.

Given what you've said, I'd have to agree with brf that making a major upgrade to your preamp could well reveal weaknesses in the MC2505.  It's not a bad amplifier as such things go, but it is quite a bit older and limited in power.  

You might be better served taking the ~$5000 total budget that would include the sale value of the 2505 and looking at a MC7100 and C2200 combo, for example.  Talking to the guys at Audio Classics could give you other ideas, too.

Good luck & happy listening!

You do have a point, I haven’t mentioned many details about my current setup. My goals here are to eventually upgrade my entire system to something much more refined and detailed, with an expansive soundstage and full bodied midrange.

Here it is:

Tannoy XT6f floorstanding speakers
Rotel RDD-1588 DAC
Blue Sound Node 2 Media Player
Rega Elex-R Integrated Amp (Preamp out)
McIntosh MC2505 Vintage Power Amp (68 WPC)
AudioQuest RCA Cables Panther

I’d Like to start my upgrades with a very capable tube preamp. I already have a system with a polished top end (which I love), and descent bottom end (could be a little tighter). I’d love to improve the soundstage depth and width, as well as the midrange response and detail.

Oh and I play high res audio only, via an external hard drive for now. Eventually including a nice record player to the mix.

Whatever you buy, you should consider the scenario if/when you upgrade your amp. I have an MC2200 McIntosh amp which may or not share the same sonic qualities as your amp and I tried it with a couple of different preamp's - mostly whatever my friends were willing to bring over and try and including my own SS NAD preamp, and the best sound was from an Audible Illusions 3A. We tried it with one of my friend's ARC LS17se and for some reason we couldn't get the volume high enough for a decently loud playback. Not sure why, probably gain mismatch. None of this will probably help with your decision since my speakers are completely different from yours- ML Aerius, and I have a huge listening room, but use the data points for whatever they're worth. All in all, there are a lot of folks out there, particularly on the McIntosh forums, that claim MAC stuff sing best when mated with other MAC components.