Connect the sub to an aux out. Say aux out 1. Now open your mixer, go to buss 1, click on the buss 1 tab on the right. Now, above the master fader for buss one (all the way to the right on the mixer, right click, and name it Sub. You don't have to do this, just makes it easy to find later. Now, with buss 1 still selected, look at your mixer. Find the channels that your kick drum, and bass are in. Raise the fader for each. Remember, if your not wanting kick or bass in your FOH or monitors, make sure that the fader for bass & kick are all the way down in the Main LR mixer view. That should do it..