BAT pre with Pass Labs amp

I am considering pairing a BAT VK-51SE with a pair of Pass Labs X600s. No dealers nearby to demo this combination. Anyone have experience with this combination, or something similar? Thanks.
What speakers are you using, efficiency and load?

I own a 51se. I have listened to the Pass, but own a BAT amp.
I have the 50se and the X350 and the sound is amazing. I really don't think you can go wrong w/ this combo.
I have the VK-30SE and X-250 and they worked fine together. It would not be a weak link in that system.
I also got a Pass X250 and I am thinking of upgrading my pre-amp. Should I get a X2.5 or something from BAT? How would you compare the two?
I also have the VK-50SE & X350 combo, and I find they work very nicely together.