Are you plugging the fo cable into the right part of the strobe? A pic of your setup would be helpful....
I don't have a DS2, my strobe is an old YS90DX and I'm using an RX100 II. Your fiber optical cable should go under your strobe in the slot that has a sensor cover (not the first one). As for setting the flash in manual on your camera to test your strobe don't loose time searching for it, there's no way to do that with your camera it's always TTL. You should set the camera flash into any of the mandatory mode (fill,front or rear). Be sure your driving mode is not on Bracket :Continous (BRK:C)