I have played around with both tube pre-amps and power amps but only older ones engineered to be Hi-Fi and operating correctly. To me, outside of being limited in power, I don't find they sound any different than high performance SS amps (when evaluated level matched and blind). I am firmly in the "Tube amp sound is a myth camp".I can't say I agree because my own experience is that a tube preamp can and usually does make a difference the sound that comes out the downstream amp, including class D amps such as my own Purifi-based amp. (Granted you will likely get more "tube sound" from a tube power amp but you'll probably get more of what's bad than what's good.)
What tubes in general do that people like is added 2nd and/or 3rd order harmonic distortions. These distortions do to sound, as some people describe the effect, is to make it more "musical", "full-bodied", "organic", "liquid", or similar descriptor. What's equally important, IMO, is that these distortions also serve to mask unpleasant higher-order harmonics that would otherwise make the music "harsh", "etched", "glassy", etc..
Again IMO, it you want to used tubes to insinuate these happier distortion, the best place to do it is at the preamp stage: you get dose of the goodies without the compromises of a tube power amp in terms of lack of power, impedance sensitivity, etc.
On the other hand I have experienced and seen first hand the psychoacoustic power of tube amps and it is indeed very powerful. To maximise this effect large tube power amps, preferably mono blocks and ideally OTL, are the way to go