The 500 cx will work just fine. You have 2 x 6+2 pin PCI-e power connectors and have 34A on the 12v rail, so there shouldn't be any issues whatesoever. The PSU is 80+ rated and has a 3 yr. warranty too, so buy your GPU and enjoy
I'm running a 6850 on a Antec 380w PSU, so a 560 ti on a Corsair 500 cx is going to be a piece of cake, even with OC'ing (if that is used). Most single GPU gaming systems run around 250-350w before any OC'ing.