I do like the sound of the HD800 all in all. I just can't bear the peak. It doesn't sound sibilant to me, but rather fatuigung after a couple of minutes without me being able to point out which element of the music just caused that at all.
Normally I'd say I like neutral or extreme tunings. I like a clean midrange, so not much midbass, as much subbass as possible and a good level of treble, but I need it to be even if its that much. Pinna shouldn't be too much as well. A great example is the IE600 with good subbass and a lot of treble, but clean one. Dead-neutral tuning works well for me too such as HD560S or Softears Studio 4.
As amplifiers I have the Dx3 Pro+, Fiio K7 and Questyle M15, but none of them solves the peak without EQ.