Audio Systems: 2003 gmc 2500 bose 6 cd stacker, cd stacker, radio code

Question
I have the following system. I have music from the headphones in the back,
but noo music from the main speakers. The speakers work as I have checked
them on other sources.

Answer
reset the radio by removing the battery   if theflock on the face ,have the radio code ready ( if rds on the face ) YOU DON'T NEED A CODE  
if this don't help it is posible the radio outputs burn or the rear seat control are on and lock on headphones