Maybe slightly off topic, but are there any live sound engineer here? I don't do this full time now but getting back to it occasionally. In my world Yamaha digital mixing board are just about everywhere, and their headphone out impedance is 15 ohms, don't ask me why. Yes brining a headphone amp is an option, but really, anybody that does this job knows how unconvenient this is it's in the way, extra cabling, you don't know where to put it, and it's quite critical in festival style event since you don't have time and more and more you're only allowed a headphone sound check.
Basically I'm on the market for highish impedance closed back with good sensitivity and good isolation, I know it's not these, but I'm quite surprised at how many fellas use this or 7506s in this situation and frankly they sound like cr*p with this kind of output.