Guys- great responses- thanks. Speakers are 97 db 14-ohm Coincident 'Victory' model with Ribbon tweeter. On paper, you may be thinking even SET, but them seem to like more power, and my room is HUGE open concept. Preamp is modded Sonic Frontiers Line 3. I used to have the ARC VT-100 MKIII- that worked well with my Pre.
Should also mention this system is used for 2-ch HT as well, so I do appreciated an amp with low noise floor and good bass capabilities, which is why I decided to try the '6Moons SS favorite' Audiosector Pateks- running them in mono (balanced- sonically great on many fronts- however I do miss the 'X factor' of added tube dimensionality- particularily in the extra decay of the notes a good tube amp can bring).
I believe the Premier 12's are single-ended only, therefore not taking advantage of the fully balanced architecture of the preamp, however that is not 'make it or break it'- I would consider single-ended amps like the Premier 12's if they really ARE that good. Other than the ARC VT-100 MKIII, not sure what other fully balanced tube amps there are at under $5k used that are better than the ARC- I hear VAC makes great stuff, but $$$...