I would like to repeat my impressions from the 3 hour listening session i had with the hd 800(which had some burn in)
I don't own them and probably i will never buy them so i have no reason to try to hide any weaknesses i noticed.
I tried them with my sony dvp ns 705v,musical fidelity x can v8(no psu,stock tubes don't know which brand),monster interconnect interlink 200(nothing special)I used some rock/pop rock/pop/ballads and some other music mostly of the 70's/80's(all cd,not mp3)Some of them are a bit sibilant on some set ups i have heard them.
I agree with skylab that the mids are very good,and the vocals sound really nice with hd 800.I also agree that the soundstage and imaging were indeed very good,noticably better than the hd 600.
I had no problem regarding the bass,it was well defined,with good impact and control and i also noticed some lower bass notes that i have never noticed with the hd 600.All in all,i liked the bass responce better than my hd 600's.(hd 600 sounds a bit muddy in comparison)
Regarding the treble now,i dissagree with skylab.I didn't find the treble to be hot or sibilant,at least compared to my almost 7 years old hd 600.I found it to be very clear,detailed and i didn't feel that the treble was too emphasized or harsh.(and i'm pretty sensitive to sibilance/harsh treble,i've experienced sibilance with my hd 600 many times in the past)
Now the downsides:I noticed a slight metalic feel in the upper mids/treble and a very slight hollow effect(sorry for my english)that it seemed to be associated with the sound stage,or like the soundstage was a bit like a 3d effect aplied with some software or something like this anyway,and it felt like not 100% right to my ears.It was like some instuments didn't have the body or the right weight as they should be.Like they were a bit distand but without the overall sound being laidback.
But i guess these downsides may be related to my lesser quality equipment(player,cables,no psu,stock tubes)although i've seen some other members here reporting this "metalic" treble and "hollow feel".