I've been listening to these for two days now and figured I'd post some very early impressions. Don't hate me for it, but they don't quite have my preferred signature (more on this later).
Out of the Sansa Clip+ (which is ruler flat and can drive even the HD-598 and my DJ100) the bass is a bit sloppy and there's too much mid-bass IMO (for my preferences). I found it way above what would be considered neutral. More mid-bass than even the HD-600 and my DJ100 (IMO). The lower mids (I believe) were very fatiguing for me. I must be sensitive to this area. Listen to the first few seconds of "Wyona's Big Brown Beaver" from Primus to see what I mean. It drives my ears nut. I would say there is not quite enough treble for me. That mid-bass doesn't always show up and annoy me and it's all random. On some songs it's fine. The sound also seems a bit congested at times. Very slightly muffled, but only at random it seems.
From out of nowhere I hooked up my Sansa Clip+ to my Airhead. The best i've heard it by far and not a subtle improvement for me. That bass is now well controlled and not overkill at all. I would say it still has a fairly large mid-bass hump, but not enough to annoy me. Perfectly acceptable. Maybe it's not so much that it's too huge for me, but perhaps not well controlled enough? The mids are now not so fatiguing. I checked the same sound above and it's still fatiguing, but made it to be a lot more bearable.
I listened to these with an amp and like them quite a bit now. These definitely benefit from amping to my ears. I didn't like them with the E10 at all, but the Airhead was nice. I'll have to try them with my E5 and X-Fi Go Pro DAC/amp. Listening to the "Buena Vista Social Club" and the "Mishima" soundtrack is pretty impressive. Even the soundstage is good!
NOTE: The bass wasn't caused by too much clamping force or anything.
Also..i'll try them out my iaudio 7. Maybe they will sound better without an amp using that source. It may be slightly more powerful than my Clip+. If this is what it takes, then that's crazy! I guess ohm ratings don't mean everything.
Edited by tdockweiler - 8/21/12 at 8:11am