Another post for future Howard, which may be useful to other people with a very specific set of circumstances. Namely: you’re running Snow Leopard on a Gigabyte P35-DS4 with a GeForce 8800 GTX 768MB in the first PCIE slot, and a GeForce 8800 GTS 320MB in the second.
The PciRoot addresses you need for those cards on this board are:
PciRoot(0x1)/Pci(0x1c,0x0)/Pci(0x0,0x0) for the GTS in slot one.
PciRoot(0x1)/Pci(0x1,0x0)/Pci(0x0,0x0) for the GTX in slot two (PEG2).
You’ll need this for when you generate the EFI hex string in EFI Studio.
Remember also to change the BIOS to boot from PEG2.
Maybe that’ll save someone else the pain of pulling the cards and running
gfxutil -f display on each one!