I was able to get into Service Mode using the following:

1. Turn key to accessory position.
2. Then press MENU.
3. Go to the SETTINGS mode (8-10 seconds).

From this Sevice Mode screen there is no Audio settings. The one I was looking to change is the GAL. I see the following choices:

Onboard Computer
NAVIGATION/GRAPHIC ELEMENT
Video Module
GPS
Sensor Check
Telematic Settings

I have been in each one and do not see the setting choice for the radio settings. Any Ideas?