Audi S4

I'm not sure if this is a proper question here. I recently installed the Clarion dvs9755z dvd player into my SUV. It's a phenomenal dvd player, really too good for what I'm doing. I have retained my stock stereo setup and listen to the dvd playback via an FM modulator. The problem is that my player is reading the discs in Dolby digital 5.1 but I'm only hearing one of the five channels. Basically the fm modulator is broadcasting only one fifth of the audio and obviously that just won't do. Should I hardwire the player or would the problem not go away. I can't believe there isn't some way to broadcast movies in stereo but that appears to be the case. Thanks much for any help.