I've been doing some comparison between my pair of HifiMAN HE-500 and a pair of Atticus I just purchased from a fellow Hear-fi-er. Here is the post I made in a different thread:
I think I made a mistake.
I removed the 1/4" TRS connector that came with the Atticus I bought a couple of weeks ago and replaced it with a 4-pin XLR. Then, to compound my error, I plugged those headphones directly into my Mjolnir. Things are really complicated now. I had been operating with the thought that I'd grow tired of the Atticus soon, it's just too closed in compared to the HE-500 for me to get comfortable with it.
Yeah, OK, that's playing single ended with a small head phone amp. Enter balanced operation with an amp that has effectively unlimited power. Gone is the disjointed sound stage I commented about earlier in this thread. Welcome really fat, round bass that still has detail and finesse. The treble is still a little recessed (farther back in the soundstage and seemingly lower in level, rather than lacking extension) compared to my HE-500s, but there is some sparkle there. I had really thought, based on first impressions, this was going to turn out to be easy, but not so.
The single song the struck me the most last night was Led Zeppelin's "Ten Years Gone", a long time favorite of mine. The first part is plaintive and almost delicate, something the HE-500s convey well, but now so do the Atticus. The Atticus present Jones' bass as heavy and full while still allowing the overtones of the vibrating strings to be heard. It's not a "one note" simplistic presentation. While I can hear the complexities of bass notes even better with my HE-500, the sound is leaner with less weight. The Atticus also does a really good job showing off all the weird stereo effects Led Zeppelin used on their recordings: "here, listen to Jimmy's acoustic guitar, it's way up here above your left ear", "Robert is singing in your right ear, no wait, now he's in the middle of your head". Not the same extent with "Ten Years Gone" as with "Whole Lotta Love" (that song through headphones almost makes me sea sick), but still there. One thing, and an original premise of my original post, is I've found the HE-500 do have some impact ability, just at higher volume than I had been using. Both my HE-500 and Atticus showed that "Ten Years Gone" doesn't really have any slam from Bonham's drum kit.
Listening, much more listening.