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.
billtro
+1 dgarretson I would use a balanced pre with one of Pass Labs balanced amps. The XA25 is single ended. 
@mesch

I got these details from Aric: the upgraded "Special" has: "Miflex PIO capacitors, all film cap power supply, heavy choke filtering, damper plates for the 6SN7s and features the Vishay resistors as well, but it has the standard iron-core transformers and ALPS remote volume control."
@billtro please excuse my short sidestep to your thread. Wish you the best in your search. 
Thanks 1markr! One day I may talk to Aric regarding upgrade. Love my Special as designed. 
One needs to know what one wants to achieve prior to throwing resources into upgrades. 
Boulder power amps and Focal speakers are a match made in heaven.
I use a Wavac pre amp with my 2060 but also looked closely at VAC pre amps.
Sonically the Wavac - Boulder combo is spectacular, but on paper there are better matched preamps for the Boulder
I’ve run my First Sound preamp with both the X150.8 and the X250.8 with great success.  Outstanding match in all sonic regards.