Hello, and sorry for the late reply.
I just recently completed a small electrostatic speaker (not a headphone, sorry.)
Good news is: SPACE BLANKET WORKED. Sounded great, played well, a little arcing didn't destroy it completely.
Bad news is: I am not an ESL professional. It sounded great, but I haven't ever heard another ESL. Also, I tensioned/assembled it very poorly. It was only stretched about 0.7% and there was a small wrinkle in the corner.
Setup: ~2500kV ballast with 15 megaohms of resistance and 1/16 inch d/s spacing on a 5inch x 7inch speaker.
Have a nice day: