For those considering aftermarket cables - you might want to take a few minutes to peruse a couple of the threads which discuss soldering hd800 connectors. In summary, as I understand it, the pins within the hd800 connectors are so tiny that it is physically impossible for large guage (e.g. 18awg) cables sold by certain retailers to be fully attached to them... This has led to some interesting comments and questions by a number of head-fi veterans and even MOT's as to what's really going on underneath the heatshrink. http://www.head-fi.org/t/467620/hd800-connectors-are-you-kidding-me/30
I've been reading up on this because I plan to either buy or diy a cable with a 4 pin xlr connector to use with my incoming bh mainline (so note that I am not a true cable naysayer).
That said, hyperbole and suggestions that exotic cables will shift frequency response and tame the hd800's 6khz mini-peak have to be taken with a grain of salt. If true, this is something that would clearly show up in software like diffmaker, but reputable cable makers are generally candid about the fact that the improvements they believe their cables bring about can't be measured by traditional means. Such measurements don't tell the whole story. Look at the O2 for example, which measures like a champ but has a definite edge to its sound that probably correlates to a design based on the use of gobs of global negative feedback to drop the noise floor. Cables may well make a beneficial difference based on criteria we haven't yet developed the means to measure, but obvious changes in FR is not something anyone should be expecting in upgrading their hp cable.