What tube pre-amps pair well with Pass amps?

Does anyone have experience with this?  I'm running Focal Sopra No. 2s and I understand the Focal's pair nicely with Pass amps.  Any tube pre-amps you'd recommend for consideration? I like the classical rock, but am gravitating more to jazz, classical and vocals. I just want to try something new.  Thanks.
You may want a differential balanced preamp to bring out the best in Pass's balanced designs.  I use an AtmaSphere MP-1 preamp with XA 160.8 monoblocks and a modified XP-25 phono stage.  It sounds very clean and can be contoured to taste with tube rolling.
@1markr My pre is about 2 year old version of the Special. Bought from Aric as a demo. How was your preamp 'souped up'?
Nelson Pass doesn't design active preamps
@keithr Pass labs most certainly does build active pres: https://www.passlabs.com/product_tags/line-preamps/

The xp20 is capable of 10db of gain.

And technically Kent English is primarily in charge of designing the company's award winning preamps.
+1 dgarretson I would use a balanced pre with one of Pass Labs balanced amps. The XA25 is single ended.