Taken from the anandtech review....
"In a conversation with OCZ Technology’s guru, Tony Leach, an expert in memory interfaces and BIOS, Tony pointed out: “The changes I know about fall mainly with memory drive strength. Engineer Oskar Wu has added even more resistors this time to allow near full drive from the memory controller. He also has routed the traces for the DIMMs over 4 layers to cut crosstalk to the bare minimum. "
And
"Another major change in the Expert board is its x16 PCI-E slots. They have been moved farther apart, which facilitates the use of improved cooling. Graphics card coolers such as those manufactured by Arctic Cooling and others, certain types of water blocks, and phase change evaporators were very difficult or impossible to use on the original DFI as there just wasnÂ’t enough room to use them. The additional spacing opens up the ability for end-users to use alternative cooling methods.
The other change involves the elimination of the SLI jumper system from the original SLI-DR. The original jumper system was a bit of headache to perform and is now switched from within the BIOS."