Modwright LS 36.5 or BAT VK-51SE

Rtn1, your comment about the right system is pertinent, and it's the criteria on which my comment was primarily based.

The OP's electronics are differentially balanced, and they are about as dead nuts neutral as one can get (Esoteric digital source, Pass Labs amps and preamp). Having owned the same amps, and presently owning an Esoteric digital source with which I've used several balanced preamps, I still believe the degree of change will be rather small compared to the expense.

But...it's just my opinion, and buying a used Modwright and a used BAT and trying them would certainly answer any questions for the OP.

FYI, Last time I talked to Paul, he has developed a fully balanced Dude so contact him if interested.

Please consider that the XO.2 has a decent resale value, so moving to either the BAT, MW or Dude won't cost me much out of pocket once the XO.2 is sold.

Onward ho, Roor!

Roor- When you gonna upgrade those speakers? I'd do that before anything else.

As far as the preamp goes. I've got a Modwright SWL 9.0 and absolutely love it with my Pass Labs amp. Mine is the model below the 36.5 you are considering. I enjoy the flexibility to roll tubes and the weight and body it adds is superb.