2015 Titan Crew Cab w/ factory Rockford system. Help

So I'm not really new to aftermarket audio, I've just fallen really far behind. I'm wanting to add in some subs and want to keep the factory radio and was looking at best location for wiring in i.e. directly behind head unit best I'm guessing but, as I got looking I was seeing people mentioning the factory amp and having determine from there where to actually wire in to the diagram. Needless I'm confused like no other. At ththe moment I'm just adding in some extra bass and eventually working through re installing my components and 2nd amp for those. In my past I always chucked my factory radio and installed an aftermarket head unit and bam already had rca Jack's for lows and mid/highs. Now I've got a much newer vehicle and am lost. Part of the problem is me not wanting to go jacking up my wiring and have a sh** install/out come.

Any help with this would be more then appreciated! Thanks