Just setup a new PC (I had some help because I barely know what I'm doing but they had to leave and now I'm stuck) and having trouble getting the GTX 570s working. The mobo PCI-E cables are 12 pins at one end split off to a pair of 6+2 pin ends. The 570s are 6+8 pin. My power supply (AX-850) only has room for one PCI-E cable. There are pins free but the PCI-E cable won't fit into them. I've tried with just the one 570 but I get a blank screen. I had to disconnect the PCI-E cable just to get the onboard GPU going. I don't have a manual and Asus don't have one on their website.
Well, I got one gtx 570 working on the 2nd slot. But now I need to figure out why I can't fit another PCI-E cable into the PSU.
that corsair AX850 it's not the right PSU you need, http://www.newegg.com/Product/Product.aspx?Item=N82E16817139011 Also if your using the Asrock mainboard you posted, look on Asrock for the manual http://www.asrock.com/mb/manual.asp?Model=Z68 Extreme7 Gen3
I had my SLI GTX 570 and Corsair AX850 running with an Asus P8P67 Pro a few months ago no trouble. I didn't install that PC myself though.
Just found a pic of your PSU and it seems that you should be able to connect the cables normally for SLI. See http://www.corsair.com/media/cms/Blog/Understanding-and-Installing-Cables-to-your-AX-PSU/Pic_2.JPG The connectors in the green section are the ones to be used. Are you sure that you're using the right cables?
Remember, that ASRock suggests also using molex power connector on motherboard, when doing a SLI of high-powered cards. You can find this molex connector above first PCI-E x16 slot - it is this black one with 4 pins.