Glad to have you back. I own the ARC Ref 3. I understand the Ref 5 has the same sonic signature as the Ref 3 -- just better. Some say a lot better. I love my Ref 3. It's simply a great line stage. So, the ARC Ref 5 has my endorsement.
What about a phono pre? If you have the bucks after the Ref 5, you may want to consider the PH-8 or Ref Phono 2. I own the PH-7. I own and love the PH-7. However, as with the Ref 3/5 line stages, I understand the PH-8 and Ref Phono 2 are much better than the PH-7. My question is how is that possible -- the PH-7 is so good.
BTW, I see Ref 5 line stages come up for sale from time to time on A'gon. It's a nice way to pick up a top performer and shave $3 to $4 grand off MSRP. Don't recall seeing too many used PH-8s or Ref Phono 2s for sale. But they're kinda new. But you never know.
One last comment. As I have said on other OPs, synergy makes a big difference. I would make sure the line stage, whatever it is, be compatible with your Boulder amp. I would think a high end audio dealer could help. Or call the manufacturer of the line stage or amp, maybe both. And . . . there's no beating a home audition if your dealer allows it. Some A'gon members report that they have been able to do home auditions.
Now. . . as often happens with similar OPs looking for equipment recommendations, get ready. Every owner or manufacturer of a tube pre is about to recommend their favorite rig. Shouldn't be a surprise though. There's a lot of great gear out there.
Good luck and signing off.
