Since I was only missing one speaker and couldn't find a replacement, I moved the existing cube speaker from the dinning area to the bathroom door spot where the speaker was missing and then mounted a Polk Audio RM6751 bookshelf speaker from Amazon under the cabinet in the dining area.
The amplifier mounted behind the kick panel is a Sony XPLOD XM-604EQX and the manual can be downloaded from
Sony eSupport - XM-604EQX - Manuals / Specs / Warranty
The front left and right outputs from the amplifier go to the woofer under the couch and from there to the left and right speaker wires over the driver's seat and passenger seat. The rear left and right outputs from the amplifier go to the woofer under the refrigerator and from there to the rear left and right speaker wires in the dinning area and the doorway to the bathroom. The woofer under the refrigerator is behind what looks like a heater return grill on the refrigerator side wall.