Jideco is a company that makes many relays, control units and amps ("amp" by Nissan usually means a "really complicated relay" in layman's terms). There is an "audio amp relay" in the system, so it may be one of the "boxes." It would have four wires to it: red, black, light green w/ red tracer, red w/ green tracer.
The wires from the left RR door speaker wires changes color before it gets to the rear speaker amp. The right side wire colors stay the same, OR and B/P.
Left RR Door speaker: OR to LG, B/P to B/Y
Right RR Door Speaker: Colors stay the same: OR and B/P
If you want the audio system diagrams and schematic, send me an e-mail at email@example.com
and I'll send them to you. Put "RE: QX4 Audio" in the subject line.