There is a volume control in the navigation options, but it also works to change the volume while the navigation voice is speaking.
I think you can turn the sound down or off in nav settings or as she/he speaks, haven't found an off button yet with one touch. I assume the instructions are seen as an important feature and will cut out whatever your listening to. I never watch the screen I just listen to the lady nag me about a turning, it stops the wife doing it. I will ask the child to check and get back to you
You dont happen to know how to get the nav onto the centre display as well do you as it comes up eith navigation but cant see how to get it there