I'm also interested in Halo Acoustics though I can't find their headphones in stock at Taobao.
I also heard they're making a headphone in the 10,000 RMB range.
Merry Christmas
I made the output board for D&G and tested it with +/-400V and 845 tubes. Seems to be working as there's 44v across the cathode resistor.
I was planning on using +/-1250V but the C3M mosfet blew up on the circlotronps because 1n4007 diodes aren't rated for that voltage.
I think the metal film resistors will work, they're used on the cfaelectrostat board in google drive. It's quite a bit bigger and you need two of them for one channel.
The thick film resistors are still bit of a problem cause of drift. Even with the dn2540, turning the trimmer a little too high or low will still cause it to drift.