The Pass XP-20 is a wonderful sounding preamp and for the price just about the best. I owned one for 4 years until I sold it about a month ago.
I also own the conrad johnson GAT preamp. It really is in another hifi world as far as sound goes.its faster, more extended top and bottom, has a more expansive sounstage , especially in depth, better detail, smaller more controlled volume steps, can drive any amp tube or ss to its best and overall puts you closer to the musicians and the music.
But, it is a lot more expensive. My advice is to not listen to the GAT as that additional expense may no longer be important
Cheers