HD-800's are analytic transducers, more so than the vast majority of other headphones, perhaps they are the 'most' analytic. As such they WILL present the sound to your ears that is handed to them warts, pimples, imperfections and all. And that isn't to say they don't have a few 'eccentricities' of their own which adds even more to the mix.
I've owned HD-800's for several years now and have just recently found a combination of equipment and tweaks that to my ears lets them 'sing'. As in toe tapping, head nodding/bobbing grov'n to the tunes, for hours on end without the zizz and spit and sizzle that they used to deliver to my ears, enjoyment. And along the way they let me hear 'into' the music, the instruments and the musicians to a degree that is remarkable and most satisfying, and now even more so.
And I know just what you mean when you say "they have a treble upper high extension that is far beyond the pale, it makes it hard to enjoy music to my ears". I also put up with that listener fatigue for quite a while. And I didn't have any other phones to fall back on.
To my mind these are close to the ultimate tweaker headphones. The potential is all there but it's up to you to dial them in. And for some who figure that they have paid their $$ and so they shouldn't need to do any further tweaking, well that's wishful thinking, for many many reasons.
These transducers are VERY revealing and VERY articulate and VERY precise in delivering the electrical signal handed to them. So much so that expecting them to work on less than compatible upstream equipment will be frustrating to say the least. And like anything else when you introduce a precision element into an existing chain, the constraints and the limitations of the previous equipment will now be in your ears. And what was a balanced and pleasant sound is now, not. In short, good enough for the previous system may not be good enough for these headphones.
Sorta like putting a monster engine in an econ-0-box car and not updating the brakes or the suspension or the tires. Yeah it'll go fast, sort of, but won't stop or handle in keeping with the new found speed. A new balance needs to be found.
BUT these headphones DO NEED BREAK IN time. ≈100 hours or so just to 'settle in', at least that is what my ears told me.
Also I would STRONGLY recommend that you install either the rabid dog mod to help settle them down or the Inner fidelity Anaxilus mod 'kit' that helps with this. I have the third generation version and I eagerly await the 4th generation mod as well.
Some people don't believe in wires as having any effect. And for them they probably don't. But they do for me. And in a similar fashion the hardware that serves up the digits and bits into the DAC and amp ALL add or subtract aspects of the final sound in their own way. Sometimes this synchronistically works out such that a weakness helps to compensate for a strength or visa versa. Sometimes not.
Right now as I write this I'm breaking in some new Q audio cables. Some say they don't need any break in. My ears are telling me a different story.
So for now I'd suggest letting them burn in, install the Anaxilus mod and then see where you are. And be aware that these headphones WILL reveal just what you feed them, so if you want to get the most out of them you need to consider what you feed them, the ENTIRE chain.
Which is why I stated above "these are close to the ultimate tweaker headphones". But they will let you know, and in no uncertain terms, if there is something you need to tweak. Which means they aren't a plug-n-pray setup. To get them to 'sing', I mean REALLY 'sing' you need to get involved and fuss and tweak with the knobs and levers. It isn't necessarily 'hard' nor hard core expensive but you're diving into the deep end of the pool now so don't expect that your feet will touch the bottom like they did.
So the challenge is are you willing to step up and get them to 'sing'?
Maybe I listen to headphones far too loud, maybe I'm always amping them up beyond what is reasonable, maybe I have differing tastes in music to alot of people here, who absolutely love these headphones. But to my ears, they have a treble upper high extension that is far beyond the pale, it makes it hard to enjoy music to my ears. When they reach certain high notes they literally scream in my ears, which isn't that nice. Maybe it's my DAC and amp, I;m running an echo audiofire 8 soundcard through a matrix m-stage headphone amp, having said that i really enjoy the echo card, its sound quality is exceptional on prior headphones like the hd555 and the sennheiser hd205 which i own. Listening to music i like, alot of aphex twin, ambient, electronic music, coil, black sabbath, whatever, the initial signature seems weak in the bass, thin, apart from placement and soundstage, but it doesnt make up for it. I don't feel like I want to hear more, with enhancers, in winamp and software EQ I can sort of change the signature sound to my liking, but i still feel like im fooling myself and having paid soo much for these phones I feel somewhat dissapointed. I've only had them 4 days, maybe I will grow used to them.