Impressions!
I listened to the following on the Schiit Lyr 2, Schiit Valhalla, CORDA CLASSIC and my own ASL MG-Head OTL MK3 (with some exceptions)
Sennheiser HD650: These were my favorite headphones all day. They didn't offer the lush bass of the planars, or the soundstage and clarity of the HD800, but they nailed the mid-range and impressed me with the bass extension and impact. They handled treble with exceptional clarity, without ever being harsh, grainy, sibilant or even a tad bit glaring. They really sounded better as a whole than any other headphone I tried all day. I purchased these today and am waiting for them to ship out (this means my HE-300 will be up for sale soon)!
Audeze LCD-2.1: When I put these headphones on, I knew I'd have to get some Audeze planars at some point. The bass is absolutely incredible without ever leaking into the mid-range. It has shocking extension, fantastic impact and amazing texture in the low-end. However, they seemed to suffer a bit with getting the sound inside of my head. Instead of a sound giving me an impression that it was filling my skull, it sounded just a bit like it was around my head. It's hard to explain, but this is not a good thing. This hurt the imaging and sound stage a bit too. The mid-range and treble was incredible as well, but the lack of spaciousness really killed the experience for me.
Audeze LCD-2.2: I'd describe these as having an almost identical balance to the 2.1, but with even more impressive in the low end. The major improvement, though, is that these were able to put the sound inside my head. They were nowhere near as spacious as the 650, but not problematically cramped like the 2.1. Not sure I'd ever own this as my only cans, but I'd love to have them for the bass.
Sennheiser HD800: These were the big shocker of the group. I expected bright, and lacking in bass. These had a beautifully balanced and spacious mid-range, Neutral and exceptionally clean treble (not a hint of grain, and harshness only when the music was at fault). The bass was not exceptionally impactful, but very tight, balanced, and well-extended. The soundstage and imaging were unmatched in the meet. Sennheiser really did a great job with this one. I thought I would not like these at all, but a set of LCD-2.2 and these would make a great antithetical pair, and I'll consider owning them some day.
Sennheiser HD590: This was probably the most impressive price/performance of the group. I found them to be a bit clearer and more open than my HE-300, but just as luscious. Incredible value if you can find them used.
HiFiMan HE-560: These sounded to me like a worse pair of LCD-2.2's. Similar balance, (less bass, but stronger mids, airier treble), but these sounded a lot smaller than the LCD-2.1. It almost sounded as if the sound was coming from a single point a couple inches from each ear.
HiFiMan HE-560 with grill mod: Surprisingly, the grill mod really fixed the problem I had with them. I A/B'ed the stock and modded and was shocked. They were MUCH more spacious, and the bass really seemed to open up, filling the "background" of the music. Overall I consider these a fantastic headphone and a great alternative to the Audeze's.
Beyerdynamic T5P: I tried several Beyers on, and all were far too bright for me to give good impressions of. Well, except these. The T5P, while still brighter than my tastes like, were an exceptional headphone. Their balance reminded me of the HD800, but overall not quite as good. They were balanced throughout the mid range, and a bit light on bass but not problematically so. I was surprised to like any Beyers, but I did really enjoy these.
Grados: I tried on several, including the PS1000, and I was completely unimpressed. I couldn't get past the cold, harsh upper midrange to hear any good parts of the sound. I was thoroughly disappointed.
Other Gear:
Meier Audio Corda Daccord & Corda Classic: This was my favorite DAC/Amp combo at the meet. Exceptionally clean, smooth, balanced, and powerful. They really get out of the way and let the music come through.
Schiit Lyr 2 & Valhalla: I was completely unimpressed. They both sounded muddy and closed off to my ears.
Astell & Kern AK1000: This might have been my favorite piece of non-headphone gear at the meet. It was beautifully made with a well-designed interface. It was powerful, clear and exceptionally balanced. Too bad it's $800