Dual CPU LGA 1366 and LGA 2011 systems need an extra QPI link that the i7s lack because Intel doesn't want people to be able to build cheap dual-socket systems anymore. Xeons have the extra QPI link (some Xeon platforms have even more to support quad and eight CPU systems) that links them so that they can communicate directly and at high speed.
The reason for not being able to run 2 of them on a board comes down to some instuction sets on the processor. UP (Uni Processors) are designed to only work in a single processor set up. The Intel® Core™ i7-975 Extreme Edition or the Intel Xeon® E3-1200s are UP processors. DP (Dual Processors) are designed to work in a single or dual configuration. The Intel Xeon X5690 or Intel Xeon E5-2640 are DP processor. MP (Multi processors) are designed to be used in single or more processor configurations. The Intel Xeon E7-8870 is a MP procesor.
The best answer for using 2 socket 1366 processors in a gaming/graphics system would be a board like the Intel® workstation S5520SC and a couple Intel® Xeon® X5690, but this is an old system.