Fun thread...nice trip down memory lane, having been enamored with electrostats since the mid 70's. Thanks to all the contributors.
Sorry i can't comment on Quads; never had the chance to hear any.
But I can add some comments about Acoustat-X and ML CLS. I've had both of these in retirement since I moved into DIY with the synergy/unity/MEH bug.
This thread motivated me to set them up for a quick listen and measurement session. Nothing very serious...just set them up hastily downstairs for more of a comparative refresher than anything.
OK, first the CLS. I'm the original owner from the early 90's. The panels were replaced by ML in the early 2000's, after mine degraded heavily (as early ones were known to sometimes do). I've no idea the state of the panels today.
Immediate impression was a real lack of bass (despite a very strong room mode at around 30Hz.) I thought this might be because I've become accustomed to more than ample bass/sub power. So I pulled one of my six single 18" sealed subs used in my main room, and set it up with the CLS.
Crossover at 100Hz worked well. No problem blending sub in with CLS...I guess i've learned sub to main integration pretty well, as everything I've built with only one exception has been designed for 100Hz up, and use with sub(s).
I think taking the 100Hz and below, load off the CLS really helped them (just like it does about every dang main speaker !)
Sound was quite nice...the "stat detail" and micro dynamics were all there. Beautiful timbe. Makes for a great lower listening level rig.
Then on the the Acoustat-X. Original owner since mid-late 70's. Jim Strickland rebuilt the OTL direct drive tube amps about 10+ years ago.
Man, they still sound great...and not bass shy at all. Sometimes on a particular all-acoustic instruments type-track, I prefer the CLS. But not often, the Acoustats just do too much right...stat detail, strong SPL, and good low frequency extension.
The panels are apparently near indestructible. (Wish I felt the same about the amps lol.)
No need for the sub, and the variable HF gain/balance lets the X be dialed in to room with other need for tonal EQ.
Hey, Cheers to all you stat lovers !