2003 Expedition radio problem

I have a 2003 EB Expedition with the DVD player. The rear speakers (rear doors and 3rd row seats) put out very low volume. Even with the fader set fully to the back the volume is barely audible with the volume cranked to maximum. My dealer had the radio guys in today and they said that's normal. You cannot hear the radio or the DVD player in the rear seats. Any advice?

Thanks!

I believe the factory system is setup to prefer the wireless headphones vs. whole car sound. I opted not to get the factory unit in my '04 and am installing dual zone indash DVD/CD/MP3 player, and 1 7" monitor into the back of the front seat passenger side. Cost was around 700, I bought a no name monitor, with 11xx by 234 resolution. I hooked it (the display) to my home DVD player last night and it looked very good. Time will tell; that's why I bought just one, I only have one kid right now too, lol. In 6 months if has worked out I will buy a few more nonames and go at it.