Powering a graphics card in Mac Pro 2008

Hi all,

I just ordered the EVGA GTX 760 SC 2GB for my Mac Pro 2008. I have read everything on how to get it work on OSX but I have doubts on powering the card.

The box contains a dual 4 pin molex to 6 pin cable.

I have a mini 6 pin to 6pin cable and a 6 pin to 8 pin adapter.

Here are my thoughts on powering it.

The card asks for 170W, so it will use the 75W from the PCI-e connection and i am planning on connecting a mini 6 pin to 6 pin and then to the 6 pin to 8 pin cable adapter for the 8 pin connection on the card. This should give the additional 75W to the card. Until now I have the 150W. So, I m thinking on using the second drive 4 pin molex to provide these extra 20W. Can I split a single 4 pin drive molex with a Y splitter and then connect the dual 4 pin molex to 6 pin cable to give the additional 20W to my card through the 6 pin socket?

I am thinking of something wrong?

ps. I would like to leave the second mini 6 pin socket of the motherboard free

Thank you!