What driver is used? I might have missed it, if you said it.
Is this another Fostex T50p mod?
It's not a mod of the Fostex. They are using an OEM for the driver and housing part but it's custom tuned. I suspect their OEM is Audio-Technica, but they haven't stated that anywhere to my knowledge. They sound and look a lot like an ATH-M50(x), but I'm not certain it's the same driver.