The thing that I took note of right off the bat, was, of course, the soundstage and imaging. The instrument separation was also incredible. Compared to the AD900x (I was actually able to compare them on the spot because I had brought my AD900x with me in my backpack), the HD800 really sounded a lot more clear and transparent, while also being more detailed. The piano that I heard was placed very clearly and the position of it was much more defined. Another thing that amazed me was how I was able to hear slight reverberation of the vocals that were inaudible on the AD900x, which attests to the amount of detail the HD800 offers. The HD800 really makes the ad900x sound thick and muddled in comparison. This was all expected though, as the ad900x is in a whole different price range. Nonetheless, my short experience with the HD800 was quite enlightening, and although I wasn't as blown away as I was when I first heard the HE400, I was very impressed. The HD800 had an overall very immersive feel to it.
Another thing, they said that they had the HD800 on sale for $1100, which is $400 less than the current amazon price. I'm not sure whether that's a good price for it, but even if it is, I still wouldn't be able to afford it. Perhaps I'll need to sell my soul for it... or not.
Piano ? Really ? I'm wondering if the shops don't have some instructions to only demo with classical. stuff.
There's also an official demo sennheiser cd with mostly jazz/ classical.
Just ask for a new demo with techno, metal, I'd think you'd have less regrets for not having these hd800.
I've personally insisted for a demo with techno before buying them, and it was less impressive, than with the first classical cd they played.
It was at this point hesitating to get them.