Quoted from GPS:
Thank you MB. I assume than I would just run this off the cabinet speaker then. Do I understand correctly?
Yep. The link was for a stereo unit, so you only use one side. Get a couple of small insulated alligator clips so you can connect to the cab sub. The other side has 2 RCA outputs (again, stereo - so you only use one side) and run that to the line input on the sub or a mixer. Guys must use these for their car stereos to hook up their powered subs. There's also a ground wire which might need to be connected to the pin chassis ground if you get any hum. My AS had a hum if I turned it up, but wasn't needed at the lower level I run so I never tried that (yet).
It's really just what's called a 'balun'. If the amp's neg output is not at ground, then it's a 'Balanced' output. Whereas the Polk input is what's called 'single ended' or 'Unbalanced' - one side is ground. Hence, BALanced to UNbalanced, or 'balun' for short. The pin's amp might not like being grounded on one side.
LTG has a lot more experience then I, so he can chime too . Might not be needed, but doesn't hurt anything to install anyway. I can send pics if needed.