you're best bet is the run a aftermarket AMP and splice the speaker wire from the OEM Audio Plus subwoofer itself and connect it the to the aftermarket AMP.
Just make sure the AMP matches the OEM audio subwoofer spec wise.
You don't actually need that harness linked above.
You can use this line out converter and spliced into the factory amp in the trunk to get RCA outputs. It also has a AMP remote turn on built in.
https://www.sonicelectronix.com/item...C2.html?from=3