Have you tried the Sennheiser CH 800 S cable? I have the HD 800 (not S) and have not compared the Senn balanced cable to others, but certainly didn't find it lacking in any way and it's very well constructed. I have to admit that I seem to be less sensitive to cable changes than others.
Sennheiser HD 800 aftermarket cable
I have a pair of the HD 800 HP’s and have modded them with great improvement. I had been listening to them with WyWires platinum cable but I carelessly broke them and am now looking for something different. Does anyone have experience with Synergistic Research’s Atmosphere HP cables for the HD 800? If you like the combo please tell my why. If there’s another cable you think is a better pairing feel free to say so and please let me know why. $800 is a steep price to pay and I’d like to hear as much as possible about the SR cables before taking the leap. One good indication: I can’t find any for resale. And as 2nd interest, what about Moon Audio Black Dragon Premium cable?