Should I use mono or stereo subwoofers?

Use the stereo subwoofer setting when you have two identical subwoofers positioned near to or behind the speakers. In this situation, the stereo subwoofers augment the speakers as though they were much larger/more bass-capable speakers. Use the mono subwoofer setting when you have a single subwoofer, or a group of subwoofers that you want to correct as a single unit.