Just trying to figure out what I actually have to order from Toyota. Here is a picture of HB 4x4's 4R
This has the JBL system
My interior, without the JBL ($300 for that one panel? grumble grumble)
ARK, do you have any wider angle shots of your cargo area, it seems like the only difference is a single panel. In the JBL equipped vehicles, there's the panel with the plastic grate for the sub, in the non JBL equipped vehicles, it's a storage bin.
What I'm thinking is this - Bend over and buy the panel from Toyota, buy a speaker/amp combo same or similar to what you used, and build a custom box to mount behind the plastic panel. Then MacIver some way to mount it.