Precision 7600 - Dual NVidia Quadro 4000 - SLI?

Just bought two Precision 7600s for our multimedia office.  Ordered them with dual Quadro 4000 cards for extra muscle and assumed these cards would be configured to work together (why else?).  However, my IT guy says that they don't appear to be linked and he doesn't see an obvious way to do it.  Are we missing something?

In my research I downloaded the 7600 tech manual from Dell wich seems to indicate that both the machine and the card are SLI capable.  On the other hand, I've alsor read forum posts describing the need to purchase a "riser card" to make it work.  Can someone give me the straight skinny on why these cards aren't linked up and whether or not it's possible to do so?  Any advice would be most appreciated!

My thanks in advance for any assistance.