Asus Motherboard A8N-SLI Premium - Manual (Page 176)

6-8 Chapter 6: NVIDIA ® SLI™ technology support
7. Click the slider to display the following
screen, then select the SLI multi-GPU
item.
Slider
5. From the Display Properties
dialog box, select the Settings
tab then click Advanced.
6. Select the NVIDIA GeForce tab.