Hello, I read your post about installing GeForce GTX760 in MacPro. I want to do the same thing and I have some problems. I do not understand why you say that "I needed a grand total of three six-pin cables". The motherboard of mac has two six-pin connectors, the graphic card has one six-pin and one 8-pin connectors. So you (I) need one six-to-six and one eight-to-six cables. Is this not right ? Thank you for you answer. Best,

 The Mac Pros have the funky micro 6 pin adapters (same as the Mac G5s from yesteryear), the trick is utilizing both the 6 pin adapters. So one port will connect to the 6 pin, and the other port will need a Y adapter for 6 to 8 pin, and then back to the graphics card. My graphics card came with a Y adapter for 6 to 8 pin adapter so I only had to get another micro 6 pin to regular 6 PCIe adapter.

The nVidia model is the exact one I used since it has a built-in Y adapter, which is required for any 8 pin to 6 adapters are all are Y too.

I hope this makes sense.