I'm having a hard time estimating the level of difficulty to insulate both the mainboard as the daughterboard. Is it really necessary? If yes, to what extent? So many questions, answers will follow later, I guess.
ASUS ROG Xpander is simply a PCI-Express daughter card for the ASUS Rampage III Extreme. The circuit board comes with four PCI Express x16 slots and two Nvidia NF200 PCI-Express bridges. These circuits take the 32 available PCIe 2.0 lanes of the Intel X58 chipset and expand them to 64 lanes, divided across the four PCI Express x16 slots on the daughter board. In the end this enables you to connect four graphics cards with maximal PCIe x16 bandwidth. ASUS ROG Xpander only has one real use, to enable 4-way SLI on ASUS Rampage III Extreme. Quad-SLI with dual GTX 295 or the coming NVIDIA D12U-15 works without ROG Expander. They already have an integrated NF200 chip (also known as BR04). The reason ASUS has designed a separate daughter board for Rampage III Extreme is that Nvidia demands that motherboards supporting 4-way SLI has to use two NF200 bridge chips, and an official 4-way license key. According to our sources this adds about $100 to an already expensive motherboard.