astolfer:
Understand that you have a plentiful supply of the Telefunken 803s's, but they are brighter sounding (less warm) than the 12ax7's I suggested.
As you are limited to only trying the DR 6h30 (or "perhaps" the 6n6p) you should be able to warm up the sound by using different input/12ax7 tubes.
If you are going to contact Brent Jessee ask him about warmer sounding 12ax7's.
This said, I've yet to hear a 6h30 based preamp that I cared for though I have not auditioned contemporary models.
Years ago I compared both ARC and BAT 6922 based preamplifiers to there "then" new 6h30 based preamplifiers and the latter for both companies were bright and bleached compared to their previous 6922 based versions.
The new BAT was a bit warmer than the ARC, but neither were "musically satisfying" to my taste.
Anyway, you have the option of trying numerous 12ax7's, which is not the case with the 6h30.
Also, the holy grail type (12ax7 in this case) may not be the best/desired sound for you, which Jessee (or any good tube dealer) should be able to help you with.
In my meager system my various/favorite 2a3/12au7/12at7 tubes vary from cheap as chips (even in the current market) to more than I paid for our latest used Honda Civic (Visseaux engraved base 2a3's would cost more).
DeKay