If it isn't too late: I have the CX-7 (now upgraded) and tried a myriad of power cords on it as well as other parts of the system. I chose the Cardas GR. To describe why, I offer the following:
I was getting these cords from The Cable Company, which really helps when considering different brands. As a qualifier, I only tried cords that retailed for less than $1000. As others mentioned, most of the cords altered the sonics. Some (most) were clearly unsuitable, but it is very hard to decide when you find more than one cord you like.
I would rather not spend money on colorations (eventually having to compensate with other colorations), but this business is hardly an exact science when it comes to auditioning. On my amp (Aragon 8008BB), the two favorites were the Shunyata Taipan Helix and Cardas Golden Reference. They were quite different, however, so which was more correct? On the Ayre I clearly preferred the Cardas.
IMO, audio equipment should come out of the box sounding pretty much the way the designer intended when using the stock power cord. If I do not like it, I move on. I chose the preamp, CD player, and amp I have because I prefered them (as is) over everything I tried in the respective price ranges. They may not have been my overall favorites, but they were within the budget I had at the time.
On the CX-7, the GR really made a most positive difference, with everything sounding more complete, musical, and real. And there were no negative effects that I could hear. If this makes sense, I do not think it actually altered the sonic intent of the player, but made it better. Some of the others I tried were: Audience, Harmonic Technologies AC 10, JPS Power AC +, LAT International AC 2 (my own), MIT Shotgun AC 1 and Z cord II, Shunyata Diamondback, Copperhead, and Taipan Helix Alpha, and Synergistic Research Active AC Master Coupler X2.
Good Listening,
Glenn