Dont buy the DD RBX. For a quad core, get Apogee GTX Dtek Fuzion, or Aquaextreme MC-05 pro.
Don't you just need an inlet for the water to be fed to the block, and an outlet for the water to be carried away from the block? Why is there three?
Right. They are called 'barbs' or 'fittings' and they must match the threadding of the block itself. You must have the same tubing ID throughout your loop, and each barb must match the threadding of each item in your loop. (threadding for each block/res/rad differs)