Hello Blakep.
The issue you are having is that the BW ASW-600 does not have a power amplifier for speakers. It is only a subwoofer amplifier. The speaker wiring in the rear of this unit is pass-through only. If you are connected using the subwoofer cable, there will be no speaker signal on the "Output to Speakers" connection.
If your source audio is an amplifier then connect the speaker directly to it, or route wires from the amplifier to the rear "Input from amplifier" connections.