Looking for warm tube preamp (should pair well with Pass power amp), budget $6000

I'm running an Aric Audio Super 6SN7 right now on my Pass Labs XA30.8. Its a wonderful match. I would look into the Aric's Motherload II as its in your price range and might be worth your consideration.

Good luck

BAT, Atma-Sphere or Conrad-Johnson.

Aric Audio as @cmach pointed out. I run the Motherlode II with First Watt amps.  I find it to be an excellent pairing.  

When you say "warm preamp" I don't follow.

If you said, "warm tubes for preamp" I would follow better. But maybe there is such a thing as a "warm preamp" above and beyond the tubes put into it.

If that is true, I'd appreciate folks teaching me that.