I know to connect an aftermarket sub, you have to take the signal post amp. I'm trying to avoid splicing speaker wires, so what I want to do is: disconnect the post factory amp harness (not sure if it's male or female) and replace it with a harness that matches the pins of the factory harness, but has spliced wires on the other end .
Then connect those wires to the aftermarket amp inputs (it has high level inputs)
Then take a second harness that's reverse... Spliced wires on one end to connect from speaker outputs on aftermarket amp, and a pin connecter to plug into the one originally removed from factory amp. Basically having an amplified signal going to all the speakers.
Do any connectors like this exist?

I read this entire forum and lots of people with first gen doing something like it, but connecting to head unit instead. I know we can't do that.