My HE-400s arrived today. The short version - very, very impressive. Instrument separation and detail are pretty spectacular, and that bass is...something else. A bit sibilant, which I'm hoping will smooth out with some burn-in. Heavy, I suppose, coming from woodied Grados, although not uncomfortable, and the pads jive totally fine with my glasses.
Sounds good from my SX-626, great from my Aune MKII SE (seriously underrated piece of equipment), but what surprised the hell out of me is that they sound fantastic out of my UHA-4 (on low gain, even), which I assumed wouldn't drive these at all.
Unfortunately, the cable they sent with them is totally wonky at the plug end, and won't play out of the right ear unless bent just so. Definitely need to call Headroom tomorrow about it.
I'm not entirely sure I want or need non-IEMs at this point, but the sound these put out is going to be quite addictive. It was between these, or CTM-200s/1964-Ts, so I think I'll give it a week or so to decide. Considering how much I absolutely adore my GR07s, though, I suspect these may be keepers. Just need to get the cable issue sorted. :\