While I spent most of the time holding court at one of the DIY and Stat tables and talking with people, I did get a chance to borrow a couple of headphones from other head-fi'ers and bring them back to my table to try out.
My impressions are pretty frank, but if you don't agree feel free to take them with a grain of salt.
Stax Sigma - Really a fun headphone. The soundstage is as huge as it is artificial, but it's a fun experience just the same. They are clearly lacking in technical prowess compared to the lambdas, but they are a very enjoyable listen and would be a fun complimentary 'phone to own even though the frequency response is a little compromised.
Stax Lambda 407 - While I like the sound quality of the Lambdas a whole lot, I don't really like how the headphones touch your ears while you have them on. Comfort is a big deal to me. If the pads were a little thicker and held the headphones a bit further off the ear I'd probably like them a lot more than I do.
Sennheiser HE60 - Great tonality. Clearly they have the Sennheiser sound to them. That is a very good thing in my book. They sound kind of like an electrostatic HD600. That being said, they don't hold a candle to the upper tier Stax 007s and 009s on the technicalities. For that reason, I found them overall to be disappointing given that used pairs are priced in the same ballpark as the (clearly better) 007s.
Koss ESP-950 - Hated these. I'll leave it at that.
Sennheiser HD800 - The best dynamic money can buy if you ask me. I used to own them before I went over to the dark side (stats). I love them as much now as I did back then. If you aren't bothered by their brightness they are THE dynamic to own, no question.
Audeze LCD3 - Another head-fi'er described them to me as "heavy on the head and heavy on the ear." I agree in both regards. They heavy on the head in the sense that they are a physically heavy headphone. Together with their LCD2 bretheren I've found the comfort on the LCDs headphones overall to be a deal-breaker. They are heavy on the ear in the sense that, while technically very good, they are weighted lower tonally than what I hear as neutral. The bass is great and well controlled, but it feels like a bit too much to me.
Mr. Speakers Mad Dog - Not bad for the money. I wish I had my similarly classed Sennheiser Amperiors with me to do a proper A/B. I liked how they isolated with the new ear pads, and I thought the control over the bass was very good. That being said, where'd the midrange go?
Stax 007mk1 and 007mk2 - A couple of great headphones. I had the chance to A/B the mk2s with a pair of mk1s and they are both great headphones. I thought the mk2s were a bit etched sounding up top but had better bass than the mk1s. I thought the mk1s had a smoother sound but were slightly lighter in the bass than the mk2s. Overall, I preferred the sound of the mk1s, but both are fantastic headphones. I wish I owned a pair, but it's hard to justify owning both a pair of 007s and 009s as they are very close.
Stax 009 - My own personal pair. While other headphones may be better than them with respect to one thing or another, there is no better overall package out there if you ask me. If you like them tonally, then they are the current King. I hear them as slightly more detailed and with slightly better bass than the 007s. I would often listen to other headphones and think "that sounds nice" only to put the 9s back on and think "but the 9s sound better". I've had them a over a year now and I've never been tempted to buy another headphone.
Last but not least are the AKG-K1000 - For what they do, they are something special. They are missing that bottom octave, but for something like acoustic guitar, strings or acoustic jazz they are a magical listen. The comfort bothers me, but these will always be one of my favorites.
