Been using the HE-400 with the Asgard 2 for over a week now. Before proper break-in it sounded downright crazy. I could hear a huge bump at around 1kHz. After break-in, it got tamer. However, these cans are still pretty bright. I don't agree with the impressions that these are dark, at all. They lean slightly on the bright side of neutral, imo. I think the lack of upper mids makes them sound darker to some, but I can't get over how sibilant they can sound sometimes.
Having said that, I absolutely love the heck of these headphones - after having fixed their FR with a great EQ program. Unlike 99% of head-fiers I've come across, I literally refuse to listen to any of my headphones without EQ (not that headphones are necessarily bad sounding without it)! I strongly believe in the power of a really good EQ program. By removing spikes and dips, and extending frequencies that are rolled-off, you get a completely new and better performance out of every pair of headphones. I think the trouble is that people don't know where to start, or they don't want to go through the trouble of learning. In any case, I am absolutely in love with my A2 + HE-400 combo with my current EQ setting. No more overly relaxed upper mids, no more sibilant and fatiguing highs, and bass is more extended than ever before. Everything just sounds so much more natural than before. If I'm watching an action-filled show or movie, I'll bump up the bass even more for the adrenaline pump. Velour pads are coming soon, so I will be able to try out the Jergpad mod soon, but with a different twist - I will post photos and description after it's done. I also took out both grills and filters, without replacing them. I figured that I don't need them, since I'm very careful with my headphones anyways; and the more open and bigger soundstage with them off is worth it.
Listening to Anthony Hamilton & Elayna Boynton - Freedom, I am absolutely in love. This very well recorded song really showcases the speed, clarity, and resolution of these headphones; and the song itself is just a beautiful song, with powerful, moving lyrics, accompanied with nice instrumentation. Highly recommended for showcasing the HE-400's abilities.
Listening to Florence & The Machine albums ("Ceremonials" and "Lungs"), these headphones showcase their ability to keep up with complex passages. The plucking of each harp string sounds adequately quick, but it makes me wonder how much quicker it would sound through electrostatic headphones, with which I have no experience.
Overall, I'm super impressed with these headphones. A very very good value at $400 imo.