SLI on ATI RD580 Chipset in Action - ATI + nVIdia = Love
 

He took DFI CFX3200 DR mainboard based on CrossFire Xpress 3200 (RD580) chipset and installed two GeForce 7600 GT graphics cards from MSI. The SLI mode got mysteriously enabled, and the drivers were absolutely sure that they were working with an nForce 4 SLI X32 Intel Edition chipset. Looks like he used some special patch here