MY13 Gen5 GT Premium Sub Box Install

[Mr SocialHarm]

I have a pair of Alpine 12inch Subs lying around along with a monoblock Alpine Sub Amp that I want to install into my Gen5 sedan.
I notice that the head unit doesn't have pre-out's.
Has anyone done this yet without changing the head unit?
I was thinking of running the port from the sub box through the hole in the rear shelf when I remove the original sub.
I assume there is an amp in the car somewhere.
Been having trouble locating a wiring diagram for the car audio.