James,
Are they all separate? Usually the Sub or the speakers will carry the crossover for the
Sub. If not then you'll either need a sound card that will support a Sub, or a crossover
to separate the signal below (X Hz)...only way I know of ...
You would use the L & R Line outs on the OC, into the crossover, then L & R out to the Monitors,
and Sub out to the subwoofer. A good crossover will allow you to select the X-over frequency.