I don't believe they support sli from what i have read.
I do not see a sli bridge. From what i know to use SLI you need a bridge to connect the cards together. Now most all AMD cards lacking a crossfire bridge communicate through the pci bus. I do not think NV ever implemented that.
2600k@4693mhz firstname.lastname@example.org p67ud4b3, 2xSuperClocked560ti SLI@965core 2400mem stock volts24/7,mounted in CM HAF922.2xHTPC's 2xi3 2120 3.3ghz dual core,1xasus LP HD6570core@850 1xHIS hd7750@1150core1325mem,55"PanyVT30