What can I say after the first two hours if it had to be short? It's a (contrary to my fears, albeit exaggerated) fantastic headphone that comes closest in fullfilling the role of an allrounder (balance between fun/neutral, soundstage) of all headphones I heard. The aspired neutrality with a better low end reproduction and a more engaging/emotional sound. That's the AKG K812 Pro, not the HD 800. The AKG to me is definitely more euphonic but I can only say this due to my familiarity of my tracks that I use all over the years for evaluation and not in a direct comparison so take this with a grain of salt.
Bass body is very nice, very well-textured with deep extension and better slam. Better than the Sennheiser in fullness and impact. Listening to John Digweed - Live in Argentina is a joy, though the TH-900 is stealing the show a bit but it's a u shaped headphone after all that is also technically gifted - something that works very well with EDM.
Soundstage is a bit smaller than the HD 800 but bigger than the TH-900, somehow inbetween (towards the HD 800) but with an open character. The first thing I hoped to not be there was the infamous weak phantom center channel that plagues the lower tiers. This problem is totally absent. Center imaging is spot on with no imbalance. Damn, the imaging really is at least on par with the TH-900 in terms of separation, layering (listening to the head-fi test-cd) but going beyond that due to its open nature. The Fostex itself is already among the very best.
What struck me from the beginning and where I focussed at first was the technical abilities, for instance in giving everything a corpus when building the image. In German we'd say "plastizität", something along 3D vs 2D as in not being flat or giving instruments no body. It instantly reminded me of the HD 800 but weightier with more presence.
Anyway, I have a wide range of tracks that I know very well over the years and Gianna Nannini's IO is one of those tracks that need the right balance to work for me as in delivering her emotion.
The HE-500 still is my reference headphone (for this track) so far thanks to its beautiful balance (healthy amount of sparkle, beautiful mids, tactile bass albeit a bit undetailed but having its own charme nonetheless) but is not alone anymore now as the new contender delivers beautiful mids as well while only lacking in the upper department with its more pronounced highs. It's no HE-400 level though (the one I had certainly killed my joy very fast) and of course not something along the lines of a DT990 or Ultrasone Pro but it's definitely there.