subwoofer summing is not a feature i would recommend using. 
doug s.
Rats...the more I learn, the less I know!

If this is a passive subwoofer, powered by a mono amp, how would one combine the lower frequencies? I agree with you if this is a powered sub with stereo inputs, in which case either plate amp is summing the signals to a single voice coil or each channel is driving a separate voice coil.
I'm only asking because I'm considering the same thing for my VMPS Original Subwoofer (passive, two voice coils wires in parallel).
Thanks in advance for any clarification. I'm new to this stuff too!
Mike