ARC Ref 210 or Ayre MXR with Wilson Maxx2

Both are excellent performers , but if your looking to add warmth to a bright or sterile system the tubes would be the better choice .

I ran my Maxx 2 with a Krell FPB 600c and Spectral DMA 360 and loved both paired with them. The Krell was more dynamic, warmer and had greater headroom but the Spectral was way more detailed and truer to the source. My taste leaned to the Spectral. I've not heard any other amplifier capable of that level of detail, speed or accuracy (Nagra PMA were close as were the Linnn Klimax Solo). I've since moved to Sasha and still run the same amps. Not much experience with the amps you are looking at but figured I'd chime in as I did live with the Maxx 2 for a bit.

I have a very good friend who runs the 200 watt Audio Research Reference monoblock amps with Wilson Maxx II's in a purpose-built room. His other equipment is the Audio Research Reference 5 preamp and Reference 7 CD player, with very good Transparent cabling, and the entire system is carefully set up. I do not like most Audio Research tube amplifiers, as they use a lot of global negative feedback to control the circuit and generally do not permit individual biasing of output tubes (only banks of tubes can be biased, which requires impractically rigorous tube matching). I am very sensitive to feedback and have a difficult time tolerating amps that use it, and his system has the typical closed-in, dead sound that characterizes amps that use feedback. However, he recently bought a darTZeel power amp - I also use a darTZeel amp - and his system now sounds much more musical and more natural to me and to him. The Ayre MXR, like all Ayre equipment, does not use global feedback, and it shares the open, natural sound of the darTZeel.

I owned an Audio Research preamp for 15 years and an Audio Research CD player for four years - I have nothing against Audio Research - I have just never liked their amps for the reasons described above.

PS - It is interesting that the new Audio Research DS225 amp is a no-feedback design.

May be I am wrong, but I thing the ARC210 needs a real balanced preamplifier - I am not sure it can be used with the ACT2. Anyway I currently own ARC and have owned the ACT2 and the 350 - an excellent setup - but I thing that the two brands do not mix well - I was never pleased with the mix of cj and ARC.
BTW, the REF210 when fitted with the KT120s is a much better sounding than when using the 6550s - it seems much more open and powerful.

I believe there is a RCA to Balanced adapter sold by Ayre that can connect single ended preamp to balanced tube amp. I am not sure this connection will be optimal for use with the full balanced design of Ayre.

A variety of XLR to single-ended adapters, and vice-versa, are manufactured by Neutrix. They are not expensive. Whether they will work well with these components is unknown to me.