Trusted Reviews posted a review on the Asus A8N-SLI Premium Socket 939 Motherboard

Firstly, on this board Asus has done away with the flip chip PCB that has to be flipped round to enable SLI a on other motherboards. Instead this function is controlled by the BIOS, so that if you put in a second graphics card, it will just work. For some reason, the BIOS option, labelled AI Selector, has three settings, Auto, Single and Dual, though I’m not sure why you need the last two settings.

Asus A8N-SLI Premium Review