How do you get the rear entertainment DVD to play through audio system?

 

In my car I do like this: go into MEDIA on COMAND, choose SOUND there then rotate until you reach SWITCH SPEAKER SORCE, choose it and there's picture of four seats, then rotate to choose on of the following- front, rear right, rear left... If you choose rear right or rear left then the sound will begin to play through audio system...

 

Second photo

 

Thanks so much.