Problem of sound with 705 and DVR station

[Natneo]

Hello,

I have made a installation of my device Archos 705 Wifi 80go and a DVR station in my car.
But i have a problem with the sound by the rca output red and white color from the DVR station.
When i want to watch a film directly by the screen of Archos, i can't have the sound by the RCA. I only have the sound by the output jack headphone. I tried to change the settings in the menu of device but no result.

It's weird because in music mode, i can listen from the RCA, but no by film mode.
I can have the sound by RCA only if I pushed the button "TV LCD" but in this case i have a black screen on Archos.

Is someone know how to get the internal video on the archos 705 and audio output by RCA through the dock DVR station ?

Thank you in advance.