Disappointment with Pass Labs - I'm looking for something else

If I were you, which I'm not, I would narrow the field first.  You have some highly sensitive speakers and they can do low wattage to high.  Get a single-ended triode tube amp.  For this I would recommend Decware, but I'm admittedly partial.  From there get a nice high wattage tube amp something like a AR, McIntosh, Cary, etc.. Also get something that is a very good AB solid state.  Do this while holding onto your Pass.  From there, play all of these for extended time.  It is said that the mind wanders to what the heart wants.  I would give it a good 30 days of heavy listening, swapping in and out.  Send back or sell what you don't like.  See if you can find an audio store that will work with you on your search. Now, whatever your heart wants, start sampling amps in that genre.  You will find the one.  At least one can hope.  I currently have 5 different systems set up in my house and kind of go from one to the other.  Some are steak and potato, some are hotdogs with chili sauce and onion and one that is total gourmet.  While you might like to eat gourmet every night, why do you find yourself craving a good dog with the works?  I decided a long time ago there isn't going to be just "the one" for me.  Once you find the perfect amp for those speakers, someone will talk you into trying a different pair of speakers and its lather rinse repeat all over again, but with speakers.  Every speaker has its good, better, best amp for it.  This changes with every pair of speakers I've listened to.  Good luck in your search. 

A few days ago I am testing a stage of professional power that I have had for many years, a Crown XLS202, in fact I rescued it from a local, it did not work and I fixed it.
It's a cheap 200W amp, it's not very good but when I put it on with the Cornwalls, everything opens up dynamically, the ends come out, everything becomes big and vibrant. Interestingly, the XP12 suits him well.
So I come to the conclusion that I need a more lively amp. The Cornwalls appreciate it.

Another vote for Atma-sphere. 

I would also think that the problem lies more with the speaker than the electronics. 

I owned a XA 30.8 for a short time and could never warm to the sound. Perhaps it was attempting to serve too many masters and was good but not excellent in any category.

I think your speakers will match tube more than solid state.

You do not mention your source or if you have changed to good power cords and interconnects yet or a power conditioner dedicated line but you are talking about throwing a lot of money on gear my guess is you should concentrate on the setup of what you have you will probably learn how good the gear you already have is.