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.