Well, I don't have any experience with the Pass XP 20, but I did go from another solid state preamp, (the Ayre K-1XE), before going to the (hybrid) VTL TL-6.5 Signature.
It is a significant sonic upgrade, albeit not a huge one. (Given the esteem that the Ayre is held in, I was pleasantly surprised that the upgrade was so significant). Having those two 12AU7 tubes in the TL-6.5 really does help the soundstaging, and the background still is as quiet as the Ayre.
The VTL is feature packed in comparison to the Ayre.
I use this with my ASR Basis Exclusive phono preamp, and my (hybrid) Lamm M2.1 monoblock amps, and I love the synergy between them.
I will probably keep the TL-6.5 for many years, much as I did my Ayre.
The only concern you might have is the size of the unit. It is very deep, as it barely fits in my stereo rack.
I hope this helps.
Good luck in your search.