I haven't been able to get that function to work either. Haven't even gotten it to simply lower the volume. This is quite annoying though. As a way around it, I have set my wave volume to around 80% and the IG volume all the way up. This way at least the IG voice is slightly louder than music. Downside to this though is I have to turn up the volume twice as much as compared to the factory radio/cd. If I leave all the volumes at max, then the factory radio/cd volume matches the carpc volume...but then you can't hear the IG directions very well.
catch 22 right now.
I'd be interested in a fix as well. Tried everything I've seen in threads to get it to work, but nothing seems to work. Going to re-install everything this morning though.