Wandering the 2014 High End Show at Newport Beach California, I came across the Abyss AB-1266 headphone. It is at once the most expensive, least attractive, and likely BEST headphone that has **EVER** been made. This is a planar magnetic (vs. Stax's electrostatic design for example) headphone that frankly looks like a torture device from Rothenburg's Medieval Crime Museum. It is heavy and huge, not something you listen to in bed, but an important feature is this: the phone fits loosely on your ears; it is NOT meant to be pressed tightly against the head. To me, the design is more like a speaker next to your ear than a headphone.
That design feature I believe is the key to this phone's sound: the most airy, and least "headphony" sounding that I've heard. I listened to the Abyss driven by tube amp from Woo Electronics, and of course the room has multiple other phones to compare to, including what is considered the best non-insane
high end headphone currently, the Audeze. Versus the Audeze (less than half the cost of Abyss at $2000) the Abyss is more open, transparent, and the bass a lot tighter and more punchy. The high end is Haagen Dazs smooth. It is completely "airy" in the most spooky and enjoyable way. Surprisingly, although heavy and unwieldy, it was not that uncomfortable. The one remaining competitor to the Abyss is the big daddy of headphones Stax SR-009, which I have not listened to. Per report of a trusted reviewer, Stax SR-009 could not match the tremendous bass quality and power of the Abyss; for sure, my own (lesser) Stax does not come close in any way, shape, or form. The Abyss's bass is seriously, seriously, tight, good, and powerful.
Although I've had a few decent headphones over the years, currently Stax Electrotstatic and Grado, I've never considered myself a "headphone guy" (I think, you either are, or you are not, with headphone... but that's another topic altogether.). I have never gotten used to the soundstage inside my head, and it's harder for me to judge any given recording's spaciousness and transparency using headphone, but if I have an extra bonus, this is the one. If you ever see a pair, especially if connected to a tube amp, put it on to see what the ultimate in passion and engineering sounds like. It is ULTRA SOTA :-) at its very best.