Cable confusion with Quadro 5800 (pic)

I'm trying to install a Quadro 5800 to a pretty recent Dell XPS machine (has Core 2 Quad and 8800 GTX right now) but there seems to be some cable mixup. The current 8800 GTX is connected to two of these cables shown in the picture:

http://www.steik.org/dump/IMG_0384.jpg

However the quadro seems to accept 2x 4 pin connectors (it says on the side that "When connecting both power connectors, both must come from the same rail").

However, these 6 pin connectors do FIT.. it just leaves 2 pins open..

Is it ok to connect? Or no?

Please be sure if you answer, I don't want to fry this very very expensive card!