Ah … I was not aware of any e-stat headphones with XLR connectors. Ignore what I said then. This will drive 580v biased e-stats with either a conventional Stax 5-pin Pro connector, or via XLRs.
DO NOT connect regular headphones (dynamic, planars, etc) to this box. It’s purely for e-stats.
The “it’s not DIY” explains the better-than-normal labeling (for DIY) on the device. That surprised me, but now it makes sense. It’s a prototype, or a beta-test unit, essentially.