2016 F150, why can't I do this?
 

I have the 4" screen stereo in my SCREW.

Why can't I do this with mine? Get two of these converter things, one for front channel and one for rear.

I already have a high end 4 channel amp in my old truck, and would upgrade the 4 door speakers in the F150.

I'm not interested in having a sub amp.....just the doors.

You can do it that way. You will just need to run new wires to your speakers from your amp or better yet search for the thread that adds a small alpine amp KKP-445U behind your dash with FOR-11CK Parrot Car Kit.