I'm trying a Moon Audio Black Dragon V2 cable for my HD800 and I LOVE IT!! It makes the sometimes searing, fatiguing highs non-fatiguing but leaves them soaring and extended and exciting and natural, and doesn't
blunt any of the Sennheisers' resolution or wonderful soundstaging. For me, the Black Dragon V2 is absolutely necessary for the 800s, making them what I feel is the best sounding headphones in the market.
(I also have LCD3s, T1s, D7000s, and used to have PS1000s and bass light R10s. Yes, the 800s with the Black Dragon beat the R10s for me.)
The bass with the Black Dragon is excellent, transparent, full of bass detail, not one-note or boomy or car-stereo-like at all. The bass is actually better than the well-regarded (famed actually) LCD3 bass.