Mike - congrats on your new amps.
Your experience with low power SET amps matches mine. Ever since I first heard a top tier SET amp in my system (Ancient Audio Silver Grand Mono - $40k, 300B based SET) I cannot get this sound out of my head.
I have went through countless amps since - Lamm 1.2R, BAT 150SE, ARC Ref110/150, Spectral 260, Pass X.5 and XA.5, Burmester 911, darTZeel, Nagra VPA, Audio Note Japan (Kondo) Ongaku - but nothing could duplicate the performance of the best low powered SET. Dart was probably the closest, giving the sound which is very transparent, smooth, articulate and has outstanding microdynamics - which is why I still keep it.
If you want to persue the SET experiece further, I would try some SET amps using 300B tubes (but only those using some quality iron, rectification, p-to-p wiring throughout, exotic caps like V-Caps or AN Silver etc) or parallel 2A3 to get more headroom.
845, or even 211 tubes, as sugested by some in this thread, will simply not get you there IMO. I had the Audio Note Japan (Kondo) Ongaku on loan for a couple of weeks (211 based SET) - which is one of the finest exaples of the breed - but it was no match for Ancient Audio Silver Grand Mono in terms of resolution, decays, HF clarity and above all - microdynamics. It sounded slow and colored in comparision.