I disagree with the view that the shrill treble on the HD800s is a product of the recordings that are fed into it, for two reasons.
First, my speakers have a flat frequency response curve. When I listen to most recordings on them, it sounds like live music. Less so the HD800, unless I EQ it to reduce the treble.
Second, if you compare the frequency response curve for the HD600 vs the HD800, you'll see that the latter is much louder through the mid-treble frequencies. My experience with the HD600, as well as every review of it I've read, is that it's extremely neutral, albeit somewhat lacking in speed and detail. I have a hard time believing that the HD800 is curing a defect of the HD600 in this respect. In any case, my ears side with the HD600 response, and even more with the HD800 tuned to match its predecessor.
When I plug the HD800 to the Asus Essence STX, it has too much treble and clinical. When I plug them into the V-DACII paired with a Lake People G100 amp, it sounds very neutral with almost no treble boost. When I plug it into my Onkyo stereoamp, it's somewhere in between but still sounds good. Only the Essence STX makes it sound too piercing (and missing texture too)
HD800 changes surprisingly much.