I just traded my Cardas for an Equinox and got the Equinox in the mail today. First off, I agree with what has been said, neither of these cables transforms the HD600's into a completely different headphone, that's a little bit lofty. Either cable definitely improves upon the stock cable, that is for sure, but even there were not talking out of this world differences really. The HD600's were hailed as excellent cans before there were any replacement cables, let's not forget that.
I tend to agree with Ebonyks comments about the Equinox sounding more like a continuation of the HD600 sound. Comparitively speaking I find the Cardas cables to be different from the Equinox in a few ways. The Cardas cable sounds a tad bit lighter in the mid and upper bass region where things like bass instruments and male vocals can sound a hair light. The Cardas is a bit more revealing through the upper midrange and into the treble, brass instruments come through with more edge and cymbals sound brighter. In contrast the Equinox to my ears sounds a bit fuller overall much due in part to the thicker mid bass. As far as depth of bass and tightness I'm not hearing much difference between the two yet. The Equinox, while still open and detailed, is not as revealing and is more forgiving in the upper mids through the treble. As stated by many, I would tend to agree that the treble does sound sweeter and a bit more refined.
Soundstage wise and spatially I'd have to say it's darn close. I'm going to have to listen to some more music before calling that one. I am getting the feeling however that the Equinox might sound a little more dimensional at this point, a lot due in part to the fuller bottom end and the more reigned in upper midrange. That fullness can add more body to images and the less revealing upper mids/treble can reduces glare and hardness which can lead to a more flat sound.
It would go without saying that I find the Equinox more like the stock cable than the Cardas is (again that feeling the Equinox is a continuation of the HD600 sound). To me the Equinox sounds like a much improved stock cable where the Cardas might sound like that too but goes further and departs a bit more. As with anything it's really going to come down to which cable works best in your system and individual tastes. In my case I can tell already the Equinox works best. I don't have a stellar source and the Gilmore V2 is a very revealing and detailed amp.
That's my 2 cents for now, I'm really enjoying the Equinox thus far.