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

Yes I've heard this about Mac gear, that it stands out most when paired with other Mac gear. I hope this is true for vintage and modern combinations of Mac gear as well. But matching gain levels is another factor I hadn't considered, but now I will. I believe the c2300/ 2500 has a function that will match gain fairly accurately, someone please confirm this.

I was also considering biamping the 2505 with another 2505, and using the c2300/2500 to feed signal to both power amps (provided I decide on buying a Mac Preamp). In that scenario the pair of MC 2505's will provide over 120 WPC to each speaker.

I have had McIntosh equipment, ARC equipment and a number of combinations of the 2. My conclusion has always been that an ARC preamp and Mac amp or vice versa delivers the worst of both worlds. ARC/ARC is my personal favorite. Mac/Mac my second favorite. Far worse is any combo of the 2.

I was also considering biamping the 2505 with another 2505, and using the c2300/2500 to feed signal to both power amps

Why would you take the weakest link in your system and add another 2505?  The 2505 was Mac's first solid state design, and they have learned a lot since it's introduction.  In addition, IIRC, you cannot bridge a 2505 to run in mono, you need to run each amp in mono parallel which only increases current and not voltage, therefore, you system will not play louder than your stereo setup. 

Thanks for posting details about your system, Ruben.  Since you are running all digital sources, I'd strongly suggest you forget about the C2300 & C2500.  You would be paying for a very high-end phono section in both that you won't be using anytime soon.  While the C2500 has an excellent DAC, it is also well above your budget.  Even the C2300 is pushing that end of it.

Because you have Tannoys, you might consider going the other way around because they are comparatively efficient and stable:  Tube amp and SS preamp.  An MC75 with a D100 would get your digital from the BlueSound into a better DAC than the Rotel and you can do away with the Rega and MC2505 altogether.  Just a thought, but I suspect that you would be very, very pleased with the result and would be in your budget range.  

If you eventually choose to get into vinyl, you can look at a C48, C50 or C2500 to keep an internal DAC and get a good phono section.  Do keep in mind that vinyl is a super-geeky branch of audio and can get very expensive very fast.  It isn't just a phono section; it's a table, arm, cartridge, protractor, cleaning accessories, interconnect and more.  It's also fussy and requires a knowledge base.  Be sure you truly understand what you're opening yourself up for if you decide to take that plunge.  

With respect to mixing ARC and Mc gear, I know folks that swear by it and others that swear at it.  You'll see my rig is pretty much all Mc, but I was crafting a very specific solution that couldn't be readily accommodated by ARC (ARC was also well beyond my comfort zone price-wise).

An audition at a local Mc dealer would be a very good idea for you.  Most of them stock Mc, ARC, Sonus Faber and B&W now, and that would let you get a better handle on the kind of sound available in your budget range.  I again suggest you contact Audio Classics; they have a world of expertise dealing with your kind of situation.

Have fun & good luck!