Yes I understand the need for a switch. If you have done audio input
jack wiring, for a mono jack, they are typically 3 terminals ( one is
common ), one is switched terminal when a plug is inserted, and the
3rd is the terminal that connects to the plug (barrel or tip). The "new
source" is of course passed through the audio plug when it is inserted.
I also understand the "break before make" issue to prevent IC biurnout.