I can't find any serious reviews online. Discussion boards have mixed reviews. Even if they bump up the audio quality a bit, I've vowed to keep my cable costs under 25% of my component costs. Way out of range for my Sennheiser 6XX's.
On a technical note, I don't understand the point of using a dielectric in a headphone cable. I heard that the dielectric charge builds up over a few days and that's what provides the audible benefit in speaker cables and interconnects. As soon as you move the cable or disconnect it, the charge goes pfft and you have to start over again. I'm not a physicist so maybe I misunderstood.
I've used Cardas for interconnects and speaker cables though and they're pretty magical even at the entry level. Very liquid, sweet, and bring out all the color shadings in the music. Dark background. Maybe not the ultimate in resolution at the entry level, but extremely musical.