Here's the best way that I know of, and have used. Get the dimensions of the board. Then scribe them on a piece of cardboard and cut the cardboard to that size. Take the cardboard template and try to fit it into your case. That will tell you quick if its even possible to fit the motherboard into the case. But there's more. If the cardboard template does fit, then place your graphics cards into the approximate areas that they will occupy and see if they cause any interference.
I suppose a good question is why you want such a motherboard. Besides the expensive of the board, which will probably be high, you will have the added expense of at least three more ram sticks and one more CPU. By the way, from what I've read so far, the required CPU design is not the normal 1366 i7 CPU, but a specialized CPU that will be expensive. If you're a gamer or casual user, this board, with its added expenses, won't do you a bit of good over a normal performance board with one CPU. For one thing, games aren't made to address multiple CPUS and ram arrays. If you run business applications or are planning to make it into a serious and dedicated folding machine, then it probably would be worthwhile.
Personally, I'm thinking about getting one for my office, but I'll wait for reviews and total of the package pricing before getting any hopes up.