I had an XP20 with X350. It sounded amazing!! I am not a fan of audio research based on the few times I heard them in showrooms so I would clearly suggest the pass.
Which Pre-Amp Pass Labs or Audio Research
I`m now using The Pass X350 Power Amp and a Audio Research upgraded LS22 preamp. I`ve also used the Ref5 both preamps sound great the Ref5 was just adorable much better control etc. Im wondering would the Pass Xp20 or Xp30 be a better way to go. I`v heard the AR preamps are much better than the Pass Labs Preamps.