Have to comment briefly about what tubes do/don't do, because I think I'm reading some misconceptions here...
Yes, certain tube amps are voiced to be "warm," and some people love these amps. But just as many are voiced to be as neutral as the specific circuit topology & tubes used allow. Some types of tubes (& brands within types) lend themselves to warmth, but many others don't.
The biggest factor comes down to how the designer wants the amp to sound. And in actuality, not many want the amp to sound overwhelmingly warm, lush, all that. Tube designers are heterogeneous in their sonic tastes & intentions, just like SS amp designers.
I have a tube amp IMS now (Woo WA3)...and owned various tube amps & preamps in the past; also heard other tube amps/preamps in other systems, audio shops, etc. I will say this about tubes: all other things being equal (ie, neutral/not overtly warm SS amp compared to a neutral/not overtly warm tube amp), tubes usually do certain things that give them a special "sound" (which doesn't necessarily = warmth):
- They convey dimensionality of notes, instruments & voices with greater detail/depth/fidelity. Notes tend to sound (IMO) more real, tangible, lifelike on tubes; the timbre of voices & instruments tends to come through more strongly on tube amplification
- They usually convey the space around & between notes with greater detail/depth. This is pretty audible on acoustic music. You tend to hear the acoustic space better
- Though some tubes are renowned for rendering highs well, while some others go very low, in general (again IMO) tubes tend to nail the midrange, where most music happens
If I had an Empyrean & one of the endgame tube amps being discussed here, I wouldn't hesitate to use the tube amp with it. The odds are the interaction between Empyrean & tube amp would be far more nuanced and less predictable than this "warm" idea conveys.