DFI offers what is called "dual X-press graphics" which allows you to use two cards in the board, however, unlike SLI, only one the two cards renders anything and the second card is only used so you can have additional VGA/DVI outputs
So basically it's there so you can use more monitors, it's a pretty useless feature if you ask me, but meh
You can mod the chipset into an SLI-D board though, and then you can use the board as an SLI board once you get the bridge from somewhere