I exchanged with someone I think on this forum the idea of transformerless SET using a high voltage radio station transmitting tube such as the GM 100 which can operate at the same plate voltage electrostatic speakers use. This should sound very pure but unfortunately it would be very dangerous. Imagine the many kilo-joules stored in the B+ power supply filter going off like an M-80 if the membranes in the electrostatic speakers ever arced.
Still I esteem in great measure the sound of panel speakers. I use 833-A SET amplifiers run at 1000 Volts through Hammond 1642SE transformers on Magnepan 0.7's and they sound better to me than a pair of $130,000 box speakers I heard.