I have a used Alpine PSU-300FRN under-seat subwoofer and head-unit amp kit that is plug and play for 2010 plus non JBL 4runners. Link to more details
Alpine PSU-300FRN Powered System Upgrade for select 2010-up Toyota 4Runner without factory premium sound at Crutchfield
I purchased this for my 4runner, it was an improvement but will not make it into a HIFI concert hall. Fully functional, all wires are include to make this plug and play. What is missing is the sheet-metal screw to attach the ground lead, and the remote amp gain control. I no longer have my 4Runner so this is not needed anymore.
Asking $250 plus shipping, can also be picked up in Portland OR.
Pic Links
IMG_2427.JPG - Google Drive
IMG_2426.JPG - Google Drive
IMG_2425.JPG - Google Drive