Android phone navigation inaudible

I have the basic Prius audio system without navigation. It was easy to connect Motorola Droid Bionic bluetooth and I can make and receive calls through audio system. But there's no navigation audio (Google Maps) from either phone or A.S. when bluetooth is connected.

 

Apparently, the audio system will not automatically switch to Bluetooth when playing AM/FM or CD. You need to select "Media" and then the navigation audio and/or other phone audio output can be heard over the audio system. Phone is smart enough to fade any music playing over the phone. But if you want to listen to a CD while navigating, forget about it.