Kim mentioned in this thread that he had mixed audio working with his nav software. You might want to ask him for details...

Yes, I've done a small kernel mod to the empeg_audio3.c file which can read audio from secondary source and mix it into the player sound stream. It automatically fades the volumes, etc. Actually, it is even able to switch between tuner/pcm modes also so that if you output audio while you're in tuner mode, it'll fade the tuner volume down, switch to pcm, output the pcm, switch back to tuner and fade the volume up.

If people are interested, I can dig it up and build some sort of diff file to the current kernel empeg_audio3.c file. It probably should be get into riocar.org.

Kim