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@4915mhz CM Nepton40XL 16gb Cas9 1600mem 2x EVGA GTX770 4gb Classified cards in SLI@1280mhz Stock boost core and 1995mhz mem SBlaster Z powered by TX-850 PSU 2xHTPC's Both w/i3 2120's,1xasus LP HD6570@850core 1000 ddr3mem 1xHIS hd7750@1125core1400mem