I've purchased the board pictured below. It works well but I'm a little mystified by the function and wiring of the inputs highlighted. I am ready to put this in a case and would like to know what these do and how to go about wring them.
By default mute is connected to GND via a pull-down resistor, so you have to connect it to VCC in order to mute the outputs. You can add a simple toggle switch for it.