I'm keeping my stock HU so I need to tap my rear speaker sigals both L and R somehow. (ON MY 2000 MAX)

I tried pulling my door panel off but that come out too well. Also, I want to keep the wiring inside the car. I tried pulling the seatbelt pillars off but that was really hard and I don't want to break anything.

SOMEBODY PLEASE!! Help me get those signals.

Thanks