This thread has gone dormant, especially frustrating while my Quads were in transit.
I have received and played with my new 2905's. Amplifiers that worked with my 63s (and sounded wonderful) are not working with my 2905s. I've tried, Radford monoblocks, Vulcan (a highly regarded 80watt per side triode amplifier, 150 Ultralinear, EL 34 based), modified Dynaco Mark IIIs and more. All worked well, especially the Vulcan with the ESL 63s, but not with the 2905s.
Then I tried the solid state route, Stax Class A DA 80, OCM 200 and once again no success. I dusted off an old war horse a Harmon Kardon Citation Twelve; there was a synergy and magic there that belies the cost and vintage of the HK. A little bit bass shy but tamed, a livelyness and see thru quality that had been lacking. Even tiny graduations in volume became apparent (when a singer trails off or sings slightly louder for affect). I'm sure that I can do better than the HK but I'm going to have to borrow amplifiers to audition to avoid making a big mistake.
What should work hasn't and what shouldn't has. Ah, it's what keeps the hobby so interesing. Although I'm a tube afficianato I'm willing to stay open minded enough to use a solid state solution, if superior. Anyone else with experience with the 2905 and/or suggestions would be welcomed.