Sorry, but off these two setups, I'm listening to what my ears are telling me, and what my ears are telling me is when these headphones are at their pinnacle when it comes to performance (if Cavalli and Manley are not the best, or at least, very high-end, then I don't know what to think anymore), they are very comparable when it comes to sonic technicality.
For a headphone to be better than one another, IMHO, it needs to best it in it's respectable category, and the HD800 and the HE-500 are divided.
The HE-500 has much more articulated bass, better slam and impact, faster transients, and a greater overall sense of speed, the usual planar magnetic sound. So, for me, the HE-500 is better at bass. The HD800's midrange doesn't have body and fullness like the HD800, it's overly clear, excruciatingly revealing, and thin. So, for me, the HE-500 has a better and more enjoyable midrange. The HD800 bests the HE-500 when it comes to imaging, soundstage, and detail extraction, and that's the jist of it, it's not an overall better headphone, it's a different flavor of high-end.
EDIT: I think the only reason that the HE-500 doesn't get a lot of the respect it deserves Is because of improper amplification. Even though the HE-6 is a power hungry monster, the HE-500 isn't far off. They are identical headphones, one uses gold, one uses silver (or aluminum? I can't remember). Give the HE-500 the power it deserves and it will easily rival headphones like the HE-6, HD800, LCD-2/3, and others.
Edited by Austin Morrow - 12/30/13 at 9:45am