[Saintly]

Hi,
the issue will be in the setup of your AV receiver. What I think is going on is that your DVD channel is set (on the receiver) to output as 5.1 surround. The port that you are using for the iPod is set to output stereo.
Try going through the options in your receiver to find the menu for sound output. I had a simular issue with my unit when I first got it where my DVD player only outputted stereo.
You may have to use your remote to get to the correct menu (on some units).
Hope this helps