2) What about a "cover" that connects power to the tuner and
amp (through a switch) , sends an init-string and "joins" the
tuner-line-out to the car's speaker wires? (Maybe a "dumb" volume control as well)
The connector may be expensive, but I guess the rest would be cheap?
It'd be about $699 US, if you are referring to the tuner module for the empeg.
It doesn't output an analog signal, it sends the FM multiplex to the empeg, where the empeg's DSP takes it and makes it the commercial ridden over corrected fm-boosted signal we call radio.
Without the Empeg, the tuner module is useless.... besides, how would you change the station?
If you are talking about a second head unit, then Sony makes a switch that will swap your outputs.