I’m surprised nobody’s answered this but if you’re gonna hook up an aftermarket amp and aftermarket rear subs, if you have the Alpine system that has the factory rear subwoofer, you could just use those two speaker wires that go to that factory rear subwoofer. That’s what I did. At the time, I didn’t use any kind of a line output converter, I just basically ran two speaker wires to the factory rear subwoofer wiring and then put RCA plugs on the end of those wires and plugged those into my amp and then tuned it that way and it actually worked pretty good.