Seems like I'm only hearing the Nav voice from the rear speakers and thus at higher volumes of music, am not able to make out what she's saying many times.

07 TL

Is this normal? Anyway to fix it or have the music dimmed even further to allow for better clarity of the Nav's voice?

 

The Navi voice doesn't come from the rear speakers. While listening to music and the navi comes on it dims the front speakers down and the voice comes out of the center speaker on the dashboard located near the front windshield. The rear speakers still play music at normal volume

Try pressing settings and turning the volume up. Each time you press volume up or down you will hear a beep that will indicate how loud the tone will be.