What tube pre-amps pair well with Pass amps?

You've got a smattering of responses and I'll add mine. When looking for a pre to pair with my first watt f4, I read a lot about tubes and topologies and eventually settled on 6sn7 based units. If you want a balanced design, I'd look at atma-sphere's offerings. For single ended, I was choosing between de Havilland, Don Sachs, and supratek. I eventually ended up with the Don Sachs and it improved everything about my system performance. Didn't get to demo the competition, but from the reviews, I don't think you can go wrong with any of those choices. The 6sn7 is nicely linear and sweet. I'll probably still try out a supratek at some point...

I heard the pass xa25 with Backert tube pream it’s a superb combo , all the accolades you mentioned were all there and some...

A few iterations back, I had a pair of Sopra II's, the Pass XA60.8's, and Aric Audio's Motherlode preamp...it sounded fantastic! Fast forward to today, and the only piece of gear still in the system is The Motherlode. Call Aric and you will not be disappointed. 

+1 laaudionut. I own the Aric Audio Special preamp. Using it now with a BEL 1001 MK5. Plan on getting a Pass XA25 in the future.