Thanks, guys.
Blueman2, the custom electrostatic drivers are indeed my creation -- they were inspired by Chinsettawong in his DIY Electrostatic Headphones forum on Head-fi.org (https://www.head-fi.org/threads/my-diy-electrostatic-headphones.498292/), and they were the reason why I started building electrostatic amps in the first place. When I saw that thread several years ago, I bought an old stax SRM-1/Mk2 from eBay to start my DIY headphone attempt, wasn't happy with the old stax amp, so built the KGSSHV... It's been an ongoing fall down the rabbit hole since then.
The drivers were made from pcb boards and mylar film with a coating of staticide 6500 antistatic spray on the film. I'm waiting to get access to a machine shop or at least a cnc router again so I can build the cups for them -- or at least get some time again to finish up the wood cups that chinsettawong gave me so I can finally case some of my drivers. In the meantime, though, I have some acrylic headphone cups I've just finished cutting that will finally serve as my version 1.0 of the DIY headphones. (will post pics soon) I know most of you guys have the top-of-the-line Stax headphones and look down on the SR-404 and 300 series, but that's all I have, and these DIY drivers blow those old Stax headphones away in both transparency and soundstage.
JoaMat, the relay board is just a stock selector board to let me switch between the balanced (tiny XLR) and unbalanced (phono) input. That and the SumR transformer are the only major components that's stock -- I made everything else from scratch including the stax connectors, pot board, etc. The stax connectors were made from stocks of teflon and have gold-plated brass vacuum tube sockets for connectors. I even molded the stax connector on the cable from scratch: the flat cable itself was a Koss extension cable; the connector on the end was made from pieces of brass rods, a teflon core I milled on a table-top cnc, and covered in a cast hard urethane casing. I DIY cast the mold out of silicon from the end of the cable on my SR-404.