Factory System, Aftermarket Powered Subwoofer

Hello all, its been awhile. But anyway Im looking to purchase a Rockford Fosgate P300-12, to give my system some extra bass. Factory subwoofer just isnt cutting it. The car is an Audi A4 (2010) with a stock stereo. It does however , have a factory amp, with a subwoofer as i previously said. My question is, should I use a LOC or the High Level Input on the Powered Enclosure? And which either one you recommend, do I just T Tap into the existing factory subwoofer wire, or cut it completely and splice it?

On the High Level Input as well as an LOC, there are multiple wires. I just want to hook the aftermarket powered subwoofer up. Do I have to utilize all the wires?

Thanks!