I've spent the last two months trying to figure out how exactly to get a Sapphire 7970 6GB (http://www.sapphiretech.com/presentation/product/?cid=1&gid=3&sgid=1157&pid=1483 &lid=1) working in a 2013 Mac Pro 5,1 running 10.8.5. Others have reported success with this card and just about very other 7970 variant, but I've been through unending nonsense just getting information about and procuring all the right components and connectors to wire this thing up, as I'm reluctant to use 6-pin to 8-pin power adaptors and run the risk of burning something out. Despite this, I'm unable to get the card working at all - fans don't spin, LEDs don't light up, Mac doesn't boot... Nothing. There's clearly something I'm still missing. I've missed a whole lot of things during this little saga, and I've had to learn quite a lot quite quickly - dozens of hours looking for information about this subject that I would have thought would be easy to find but wasn't, with plenty of little caveats that are so easily missed. I'll skip all the ridiculous details and simply explain where I'm at now, so I can get past this last little whatever-it-is I seem to still be ignorant about. Right now, I've got an additional PSU (http://www.newegg.ca/Product/Product.aspx?Item=N82E16817151099) sitting on top of the case, with two PCI-e 6+2-pin connectors running to the card, which is seated in the x16 PCI-e slot. The PSU's power switch is set to I (on), but it doesn't seem to be drawing any power. Here's where I may be missing something. Does the PSU require something else to tell it to begin doing its thing? I got this PSU as a replacement for a previous PSU I'd purchased for the 7970, which had no switch at all and required power from a 4-pin Molex to tell it to begin drawing from AC, and since Molex isn't included with the 5,1... Ehhh.... This new PSU was purchased specifically because it has a simple power switch. Now it seems I may have just thrown my money out the window twice on two PSUs. Does this thing require a blood sacrifice or some sort of dance? What's not right? Alternately, all I can think of is that the card is trash and a crooked eBay vendor has now gotten off scot free, considering how long it's taken me just to determine that the card isn't working - far too late for buyer protection to still be applicable. Help?