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

I have a Pass 250.8 on a pair of Wilson Sabrina in a neutral treated room. I run a Pass XP 10 pre amp and the system is neutral or possibly leans toward the warm side. I'd think that it'd be too warm if a warm pre amp was added into the system given the Pass amp. it may be more of a room treatment issue you have  if you find it too bright- or your speakers ? Changing the pre amp out for 6k to possibly gain a slightly warmer sound may not be the best bang, nor the most predictable means of testing things out. Try the EQ settings in Roon if you use it. They're very flexible, you can set many different bands up with varying Q factors, even set pre set curves for low level, loud listening and much more. It's included with Roon.

Why tube in a dac ? I have had several Lampi dacs they are smooth but you loose resolution . A very good R2R dac has better resolution  for a great example 

I bought one, the Denafrips a terminator2 

will give you Everythung you could want and more and it’s only $4700.

the terminator+ is slightly better but $6500  both are pretty much the same except for a few capacitirs , a rounded edge on the Terminstor+ and even tighter specs way beyond hearing . TheTerminstor2 ,and weighs 42 lbs and yes there are service centers in theUS  now , which rare ,very dependable and built like a tank  with all brand name quality parts.

I run a Aesthetix Calypso Signature into a Pass Labs x350.8 about half the time when i want to go 'warm'. I switch that out between the xp-30 as my silly whims change month over month.  Plenty of gain, no compatibility issues, and is super sweet.  I usually run early 50s mullard or 60s amperex to adjust the 'warmness' in both the 12ax7 and 6dj8 positions, although OEM tubes work just fine.  Playback is going through some Wilson DAWs. It's great too since it has HT passthrough and doesn't need to be on to watch TV or do movies.  Plenty of inputs and outputs too....

Surprised nobody has suggested the Modwright LS100.  I have owned and run McIntosh C2300, C500T and the Aesthetix Calypso Sig and I prefer the LS100.  I run NOS Melz 1578(6SN7) tubes and NOS Mullard GZ37 Fat Bottle and the sound is magical.  Currently paired with Odyssey Monoblocks and couldn't be happier.  New pricing still under your budget and used way under your budget with plenty left over for tube rolling:)

for warmth I second either of the Cary SLPs