Any word about this fella?
He's got some silver cables for the HD600 that are... interesting. I'm wanting a second cable as a 'just in case' and while the 3.5-terminated cable is $40 more than an OEM Sennheiser cable, the interest is still there to see if I can hear a difference through AB tests.
I don't know anything about those cables, except that they're purdy. But hell, at those prices you could afford to find out if they're built well or not. I don't ever advise anyone to buy a cable in hopes of getting any performance gains. A/B testing is tricky business and should ONLY be done with the help of a friend so that you don't know which cable your listening to. It's very easy to trick yourself into thinking you're hearing things you want to and having any sort of bias, even if you're not consciously aware of it, is fuel for imagined qualities or lack thereof.
If you'd like to try different cables I always recommend building them. It's very easy to do, inexpensive, fun and a great way to customize your headphones. There are dozens of patterns of paracord you can use for the outer shell and you don't need to buy expensive DIY wire, CAT5 network cable does just fine.