What model of Rosewill? If it is fairly new, it should already have 2 6-pin PCIe connectors.
Sounds like you want to use a molex to PCIe adapter cable. Is that correct?
I do have 2 pci-e connections on my PSU (factory connections, not adaptors) but they are running off the same cable, I was wondering if that was common to use for a graphics card or if it was too much power for one cable.
They will be fine. Now I understand. Have fun.
(btw, its a RD 550N Stallion if that makes a difference at all.)