To clarify a little more: "LD_SW" and "REST_SW" and "CD OPEN SW" are obviously switches, but they are each just one pin -- how does the circuitry know whether the switch is open or closed? Where is the "other side" of the switch? How do I fake open or closed?
I have had partial success modifying a small all-in-one hifi without aux-in (a Panasonic SA-PM21) to support a Bluetooth receiver. It is successfully playing Bluetooth audio, but only when I have a CD inserted and press "Play".
Clearly there is circuitry in place that kills amplification until...