I've done some more seaching, and looking through the the skin commands.
I see where I can cycle the mute state of any line in windows, but I cant see a way to unmute or mute irrespective of the current state.
eg. say it is already active and I send the command to unmute, then it would stay as it is.
Also is it likely I will be able to have the line-in muted for GPS directions and Phoco?