Listening to these for a bit I think I've figured out what the mid HD sounds like. Vocals above bass/baritone sound distorted in a way that's reminiscent of the Black Keys' vocal distortion effects. I'm not sure how the Keys model it, whether through a tube "warmer" or saturation, but it's unlike old recordings in that the vocals don't sound quite as bandwidth limited. The HE400's distortion also serves to bring up compression artifacts, both dynamic compression and, oddly, mp3 compression. Maybe part of it is a raised noisefloor, I think it might be that the added HD noise might have an etching-like effect, though not necessarily in the negative implication of that word, more like coin etching --
This added "grain" works for some of the pop recordings I've tried. For purely electronic compositions it adds an almost smeared transient-like quality to some samples, again kind of like a sequencer is messing up playing a sample. Thankfully the HD doesn't appear to compromise up the sense of instrument separation.
Tonally the headphone is not bad at all, I like the moderate V-shaped response, it reminds me a little of an exaggerated 007. A bit more slam than the stats while maintaining all the detail. I've heard "faster" bass from stats (009) and other orthos (Abyss, maybe the LCD3), but this is a very good balance.
The soundstage isn't as closed in as with the LCD2, although it doesn't approach the diffusivity of open dynamics.
