That's what I'm saying, you won't be able to put that into the 8 pin port. You could however put it into one of the 6 pin ports. Only problem is, I don't know which HX PSU you have. The HX-1000w, which I have, has 2 rails. It's practically two 500w PSUs in one. Which would be problematic if you have too many things on one rail, as in you couldn't attach 500w or more of stuff on one rail. Again, this applies to the HX-1000w, the lower watt versions might be different. Reference:
http://forum.corsair.com/v3/showthread.php?t=70317
You could get a pin remover from frozencpu and buy an 8 pin connector from their DYI section. Buy the cable, remove the 6 pin connecter which has the pin, and swap it with the 8 pin. You have to make sure to get the female connecter, the one with the pin in the center.