Thanks, mate. I need to do a lot more of those primers .... (fucking rapper cans.)
I tend to think the reference of live sound is hard to translate to headphones. One thing I think does translate well is the human voice.
It's something we hear a LOT, so we're naturally familiar with it. I think extraordinarily so.
So I like to listen to vocals carefully, listening to the timbre of the voice and how convincingly real it is.
Other than that, I think the best thing you can have when evaluating headphones is having heard a LOT of them.
I also think Steve Guttenberg was right in his article at innerfideilty about his reference tracks:
that extreme familiarity with personal set of very good recordings used specifically for evaluation is important.
Combine lots of experience with headphones and the personal test tracks, and it can be a pretty quick process to get a "read" on a pair of headphones.