Are you saying the step up transformers in Quads can be bypassed?
Actually, I meant that remark in the sense that there's nothing inherently "wrong" with the fact that tubes have relatively high impedance characteristics . . . it's just very different than the low impedances of dynamic loudspeakers.
For a high-impedance (i.e. electrostatic) loudspeaker, then there are indeed methods for directly coupling a tube amp to its electrodes, and a very efficient transfer of power is possible . . . Acoustat did this in the late-1970s, with very well-received, albiet unreliable results . . . I serviced a few of these many years ago, and can personally attest to both of these characteristics.
A direct-drive electrostat these days is still a pretty intimidating engineering project - the best common tubes suitable for the task (i.e. TV sweep tubes) are long out of production, and custom transformer(s) will probably still be required, for the high-voltage supply. And if you're talking about the ESL-63s, there's the bit about the multi-tapped delay line that would probably be a complicating factor.
If I wanted to build an active electrostatic speaker with a tube amp, I'd probably look more to using a conventional push-pull output stage with conventional, readily-available audio tubes, with a special low-ratio step-UP output transformer to match the electrostatic panel. But it'd still be a LOT of work to get it right.
