The plugs on the cable there allow for two optical(dvd/cd) not two hard drives with the small plugs seen on the right side there plugging onto a block of pins on the board itself. You have to go strictly by the diagram for the MSI board to locate the second or third block for those along with the first block which sees the power switch, power and hard drive leds, reset button, etc. and look for the different colored areas for each pair of plugs.
That depends on whether the unshown end goes into a sound card or the board itself. If already plugged onto the board with the other end then the small plugs are left free if one of the two black plugs are plugged into a drive.
