NAV & radio volume

I'm a new owner trying to figure out the relationship between sound on/off and volume with both the radio and NAV systems operating. I'm very pleased that the radio volume is reduced whenever the NAV system audio is "talking to me."

However, when I get close to my destination I often want to turn the radio off so I can concentrate on my driving. In my old car with a separate Garmin GPS, I would just tap the volume control on the sound system and the radio or CD would turn off. Does the built-in NAV system work the same? If I'm displaying the map directions and listening to XM radio, will tapping the volume control turn off the radio but leave the NAV audio on? I know that if I experimented long enough I could probably figure this out, but I'd rather get the benefit of others' experience.

A related question is whether the NAV volume control is independent of the the radio volume control. Does turning the volume knob affect the spoken directions from the NAV system?

Thanks in advance.

It would help if you added your model and year to your profile, and some hint at your location (at least country). What is the model number printed on the front of your factory radio? (hunt for it -- only a few models don't have one).

The car is a 2016 Legacy Limited. There's no ID on the face of the radio/display. All it says is SXM HD radio. Is there some way I can get the unit to provide its model and serial number? I know that my smart phone can do that.

On my '06 SpecB, the nav volume is set via a menu in the nav screen, the volume setting on the radio has no effect. Mine also "mutes" the radio when the nav starts directions but again, the nav speaking volume is always the same. I never tried with the radio completely off, but turning the radio down does not turn the nav speach volume down.