Just got the 2m Zu Mobius myself. Sounds excellent. I was worried that it was going to be too bright as there are many comments on head-fi about their brightness. I personally find the cable to be fairly well-balanced. I don't find them bright -- rather, that they are more extended and transparent up top. I also find that the region they have the greatest effect on is the lower midrange (200-700 Hz)... more open and transparent, a bit louder in that region.
I recall saint.panda's review: "I did notice a funny thing in the midrange. I had the feeling that the midrange got a bit warmer and more predominant, the instruments appeared bigger than on the other cables and soundstage seemed to be a little bit smaller. Maybe somebody can explain this phenomena to me". Yep, that's probably due to the 200-700 Hz region emphasis. (just to be clear, I'm not saying it's only a case of emphasis... it is also the transparency and openness... i.e., the quality, not just quantity, has been improved)
This also serves to improve the bass definition, warmth, and punch because much of our perception on bass quality is based on the bass harmonics that extend well into the midrange, not just the fundamentals in the 50-120 Hz range. And it also serves to preserve the spectral balance so that the better high frequency response doesn't cause the Mobius to sound bright.
My biggest reservation about the Mobius is the techflex covering. If you sit still, this is not a factor, but if you like to turn your head and move around a bit (getting files, paying bills, or just groovin' to the music), the cable will slide against the desk and your shirt collar and be microphonic. One day I might get brave and cut the techflex off... alcohol might be involved
I should also mention that connecting the plugs to the HD650 was a painful experience. Literally. I have just now regained feeling in my right thumb
The force required to snap the connectors into place is significant!
In short, love what the Zu Mobius does for the sound quality of the HD650. But I do feel that the Mobius is ridiculously expensive ($229 for a fricking wire). But I also grudingly admit that it is "somewhat" worth it for the improvement. The actual sonic improvement is not in question, only the price. Let's just say that if it was the same price as the Cardas ($150), I would say that it is an unquestionable value.