Against long odds, I got another chance to do some more careful listening yesterday. On a hunch, I put the Fluke on the ML2s, and, sure enough, the left channel had drifted up to 340mA and the right had moved up to 300mA. Once I dialed the operating points back to where I wanted them, I finally got to hear what I had/had not accomplished with the DEBZs and my "Powerful SETs". I was a little anxious to get in a good listen before the new caps go into shock for two months, and I have to say I have accomplished most of what I set out to do. Sure, I simply abandoned ULF, but I will not feel bad about this until someone else comes up with a way to get true FR at live volumes from one amp. Right now, I'm good to the high 30's with one amp, "approaching" live volumes; loud enough to get the message, from classical music.
Since no one but me uses full-blown, original DEBZs, this is not so much an advertisement for this speaker design as it is my own attempts to get FR from one SET amp per stereo side, just like the thread header says. Even if I keep playing with contours, I have fed my curiousity about FR with one amp, and I have in the process pushed the venerable Lowthers a good deal farther than I thought they would go. In doing all this, I believe I have come up against and gained a better understanding of the stock electrical and mechanical limits of the drivers that comprise my speaker system and, in the process I have also, finally, pushed the effective limits of the ML2s, as far as these particular speakers, at this particular point, are concerned.
Not to sum, but to recap and re-frame: I am pretty sure at this point that the range from, say, 70 Hz to high enough can be done quite well with a single powerful SET and 3 -4 "way" direct radiators, with 2 amps per stereo side. To gain dynamics and clarity over what I have now would require "better drivers" (as opposed to significantly different topology), and I have actually started working on this, very slowly. In the meantime, my DEBZs work better than ever now, by a fair margin, still a single SET amp per side.