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

The simple way is to find a pre based on 6H30 tubes.  Ayon and AR do this.  Others as well I am sure.

The 6H30 is a frame grid triode, and like all frame grid triodes (such as 6DJ8s) is prone to oscillation at some very high frequencies unless care is taken in the design. This opens them up to microphonics associated with the parasitics. Its a nice linear tube good for instrumentation but really isn't suited all that well for audio.

6h30 is too strong for preamplifier. Try to avoid this tube in preamplifier if you value harmonic sound.

6h30 works well in power amplifier.

Ref 10 is a exception as they use 4pcs each channel and independent tube rectified for each channel.

After much research I went with a Zesto Leto tube pre to go with my Mola Mola Kaluga monos. I am very happy with the result. Not sure if it fits the definition of warm, but it has made me very happy. American made and they have exceeded my expectations.

I have a Cary SLP 98 I can let you have for $2000. Let me know.