Capital Audiofest was great. Met a ton of really nice people there, very welcoming as well.
Here are some brief thoughts about each of the headphones I've tried (some not pictured.)
Abyss Diana MR: These were among my personal favorites. They're so incredibly smooth, delicate, and absurdly detailed. The bass was tight, controlled, flat, and precise. Treble is about as close to perfect as you can imagine. No brightness, nor was it muddy. It was just what you'd expect for 3,000 dollar treble response, which is near flawlessness. What struck me the most was not only the insane comfort they provided, but the midrange reproduction was phenomenal. Just stellar. No sibilance, no veil, it was just full and sounded like honey. I understand Abyss gets criticized alot, but if these headphones have one special quirk to them, it has to be those creamy smooth mids, if nothing else.
Stax X9000: What has been said about Stax that I can't already add? Single handedly the best electrostat I've ever heard, till of course I get my hands on the HE-1 or Shangri-La Sr. The detail and exquisite control of the entire spectrum is unlike anything I've ever heard. Bass is lean, which is a common trait for electrostats, but what *is* there is utmost care and precision. The same goes for the midrange and the treble. The main common theme of them is just sheer precision. The only fault which comes down to personal preferences is lean subbass, but as far as sound goes as an overall package? I'd be hard pressed to find something better than this. Even better than the Susvara to be honest.
Hifiman Susvara: These are flawed, I'll say that straight up. The treble is a bit too wonky for my liking and even as an HD800 owner, i'd know all about that. But something about its treble felt off to me. This is something that neither the Stax X9000 nor Abyss Diana had issue with. But what made my jaw drop was how unabashedly huge it sounded. Not sure if it's a driver size or something else, but the soundstage sounded huge, from a vertical scale. Not so much width (even though it was wide, just not HD800 levels of width), but things felt "large" and "tall", if that makes sense. For scores like Interstellar, Tenet, and Oppenheimer, this was VERY apparent. The bass was incredibly full, with a powerful and distinct midrange as well. I just wish the treble response wasn't as wonky as it was.
Sennheiser HD820: Oh boy, where to start with these. I think when DMS said the vocals sounded like a bluetooth speaker being drowned in a sink, I don't think he was off the mark there, at least with vocals cause HOLY SHIT it all falls apart there. The midrange is simply nonexistent. And it came to me as a shock given that this is really sennheiser's bread and butter here. I imagine there was some serious design challenges with the close off of the drivers with the glass but jesus christ. What's a shame though is that for instrumental pieces, it sounds... great actually. But the second vocals came on, I couldn't bare to listen to another second of it. Coming from an HD800, my jaw literally dropped as to how bad it was. It might be for someone out there, and I'm really happy for those who enjoy it, but man. That was rough. REALLY rough. Maybe EQ could salvage the midrange suckout, but that was painful. I wanted to like them and give them the beneifit of the doubt. They missed the mark so unbelievably hard here. I'd like to see them try to experiment with a closed HD800 again, just... not whatever the HD820 was.
Audeze LCD-5: Now THIS, is what a flagship is supposed to be. This by far in a way was the better headphone to the Susvara. Midrange was authoritative, full bodied, and crystal clear. Every speck of detail was right there for you pick out. Bass was tight, deep, and flat, classic Audeze right there. Treble is what near 6,000 dollar treble should be like, eat your heart out Hifiman. I'd even say its MORE detailed than the Hifiman. Nothing ever skipped a beat. It was effortless whatever I threw at it. Complex to simple tracks. Phenomenal headphones.
Focal Utopia: Haven't heard the original before the refresh, but as per usual from focal, they are INCREDIBLY dynamic and punchy. By far the most "alive" feeling headphone from the bunch. Bass is punchy and yet it never muddies the midrange. Very engaging too for hip hop and pop. Midrange and treble are also just so unbelievably clear. I couldn't justify spending this much for a focal when there are better options at summit-fi level prices, but for anyone looking for something more engaging than the other headphones mentioned here without sacrificing a reference sound, these are easily the best pick.
Meze Empyrean 2: I'll just keep it short and brief, but this is literally just what the Meze Empyrean should've been from the start. Easily the best of Meze's lineup. That's all I'll say here.
ZMF Atrium and Atrium Closed (With perforated lambskin pads): I want to get the Atrium closed out of the way and say I feel like ZMF missed the mark with this one. It was a bit too harsh and sibilant for my liking personally (though YMMV) and it was nowhere near as great as the Atrium Open. The Atrium open on the other hand was so tastefully colored in the midrange. That's what ALMOST sold me on them. I think part of the magic with ZMF is that they make you forget you're listening to headphones. Everything just felt "right" to me. Bass and treble were great as you'd expect, but the real creme de la crop here is the midrange, much like the Abyss Dianas. Just unbelievable. These are the ultimate lay back and forget anything matters set of cans you could possibly buy. These and the Abyss Dianas were easily my favorites BY FAR. I'm heavily even debating selling some things to buy both. They're THAT good.
Audeze LCD-X and CBRN: The CBRN was.. just alright. Middle of the road, but they just absolutely pale to what the Stax X9000 were as far as electrostats go. Maybe my impressions would've been different had I listened to these before the Stax, but unfortunately that didn't happen lol. These didn't grab me nearly as much as the LCD-X or the LCD-5. THOSE were the real stars of Audeze's lineup. The LCD-X is fantastic, especially as a "fun" sounding headphone for hip hop, EDM, and pop especially. There is a bit of EQing needed but that's kind of the quirk and charm to them. These are great pair of complimentary cans honestly. Truly great set and they're a good guilty pleasure away from the normal reference sound that can get sterile and boring after a while.
These were just brief thoughts on each of the headphones I tried there, and even tried some INSANE speaker setups that were there as well, but that isn't relevant to the sub. Honestly some really great people there who were very generous, and the headphones there, just also a very unique experience to be able to try them.