It was actually a very smart move by DFI. Think about it: One PCB design, one PCB layout, same circuit traces... for the various variations you just changed the chipsets (nForce 4 Ultra, nForce 4 SLI) and, for some boards, added an extra SATA controller and four more SATA ports (hence the "R" in the model name - "R" for "RAID"). It's a very elegant, simple, economical production design ethic employed by DFI.
Bogey, about your RAM, I'm still sorting through some sources of info. I plead for a little bit more patience.
I tend to be slow when it comes to researching; I don't want to give out bad info, you know?
Back to the LANParty boards: thlnk3r is right, of course. The older versions of the Ultra D could be modded so that SLI could be enabled on them. However, nVidia compelled DFI to alter the circuit tracings on the Ultra-Ds so that SLI could no longer be enabled. nVidia didn't want anyone to have "hacked" SLI...
So, if your Ultra D is a newer revision, it cannot be modded to support SLI.