Combining an Audio Signal and 9 VDC on the same Trace
The cheapest solution would be to use a 3 pole 5 position switch and use the 3rd pole to switch the outputs. It is possible to combine the input and DC voltage into one line, but that brings up new complications. The input signal could be coupled to the DC with a capacitor, then extracted by using a second capacitor on the amp end. Problems to overcome with that would be power supply ripple would need to be very small, and you need to deal with impedance matching on both ends. A third solution could be to use individual relays at each amp module location. The switch would energize a 2 pole relay that which would switch the input &amp; output.