Most coolers do not work with the eVGA 680i motherboard by default; There is the aforementioned metal plate on the bottom that prevents you from mounting on any non-standard heatsink. Mind you, I don't have personal experience with this as I cannot afford a $250 motherboard, but its what I've read complaints on. Most people that want to make the aftermarket coolers work have been hardcore enough to take to modding the motherboard and that plate to make the coolers fit. So you can mount aftermarket coolers on the eVGA 680i, it just takes a bit of skill (and guts).
EDIT: I'm doing a bit of research on it now (Newegg reviews are noob) and it seems like there isn't a metal plate on the back. Infact, there is the plate that comes with most aftermarket coolers that goes on the back of the motherboard that poses a problem. I should've known this as I also have a Zalman that came with one of those. The area where the backplate for the cooler is mounted has some capacitors that are likely to get crushed if you try to mount it there. People have been using a Dremel to make holes or hollow out the backplate so as to give the capacitors room. The thing that I'm looking at specifically used a Zalman cooler, so I don't know what that Newegg review was talking about.
