For me, vast improvements in sound, size, and affordability have opened up the possibility of modular preamp/power amp rigs which I never touched before, because I did not want to futz with rack gear + big/heavy amps. Even if I wanted to deal with that kind of footprint, living in NYC and makes it a huge hassle. Every square foot costs $$$, and gear size can make the difference between having to tour with a trailer or not.
I now use a Jessup Model T preamp on my pedalboard, running into the effects return of an Ampeg Micro VR head. Used this way, the Ampeg is a small, rad sounding class A/B power amp that can get moron loud with guitar (I actually have yet to try it with bass, for which I imagine it would be power enough for everything short of the idiot volumes at which my band plays). The Ampeg’s power amp does not sound flat/neutral to me, which is great; I prefer the character it imparts over the very flat/neutral sound of the Quilter head I had been using as a power amp (also running into the effects of). I have tried a number of other small tube and solid-state preamps with this rig, and I am stoked with the Jessup Model T pre. Anyone expecting it to sound exactly like an old Sunn will be disappointed, but, judged on its own merits, I think that it sounds incredible. The Jessup pre + used Ampeg Head cost less than $600/total. I have a Jessup DR-103 preamp on the way as well, and i’m eager to see how they mate up.
Also: previously, my main amps were a Marshall Superlead reissue and a Ceriatone Hiwatt DR103 Clone. Both are amazing amps; I initially got the small preamp/small power amp rig to use as a back-up. I tried this rig at a show for the hell of it, and stopped using the bigger tube amps shortly after. I now have a Bugera 1960 head (also an incredible-sounding amp, bought after Bugera seemed to have solved their reliability issues) just to have a tube amp around, but i’ve decided to part with that, now.