What External DAC pairs best with Audio Research Equipment?

If you are using tube preamp and amp , it’s worth adding a solid state DAC . My choice is the new schiit Biggy. Audition it return it if you don’t like it. It might synergize with your system. My guess it will work. That’s what I did my schiit gungnir Raysonic cdp as transport , audio research preamp and mono block tube amp and it took away softnesss and added good bass and transient.I am amazed.

Audio is full of surprises , you will never know till you try it. Most of my success mostly is when I least expected the gear will work on my system.You have to invest time trying yourself. Agoners can guide you at the end it’s  what you like.

I use a Ref 5SE in my system with a Bryston BDA3 DAC. It sounds fantastic.

While I am sure the AR DAC9 would be a great match for your AR system (and look so good), I agree with those that have recommended a more resolving DAC.  I think another warm sound is too much of a (good?) thing.  I think the amazing DAC now had for a value used is the Mola Mola Tambaqui.  Great resolution and soundstage, world acclaimed.  Can be had now for under 8k.

staying in house always gives some assurance of good matching of gear and tonality but beware that companies such as arc have been around for many many years and their gear from different decades can sound somewhat different and mate as differently as different makes of gear

second point is in my experience if you have a a fairly modern (2000 and forward) arc pre/line stage it will take the input of any modern dac just fine -- so go for what sonic flavor of dac you see fit to suit your personal musical palette