I like doing a lot of research before buying phones. Nobody has mentioned the NADs yet.
I know the feeling. But for what it's worth, I'd take InnerFidelity reviews into consideration. Tyll Hertsens is a very good reviewer. Steve Guttenberg of CNET praised (albeit in passing) the HP50s, as well. The isolation is -16dBs, so they're definitely no slouches, in that regard. The handful of Head-Fi "reviews" that I've seen (more like impressions) paint a very pretty picture. It probably seems like a precarious gamble, so if that bothers you, then buy them from somewhere you can return them. That said, while I
hate to take the opinion of one reviewer as anything resembling objective fact, if Tyll liked it, chances are you will, too.