Disco 3 DVD system

Can anyone help me out here, i have just bought a dicovery 3 HSE that has the build in DVD system on the roof, the problem is that i am trying to play it through the car speakers, it says you have to press the source button and enable car speakers then press the Aux button on the stereo, but no luck, can anyone help out, something else that might be an issue is that there is a parrat installed as well, pairing it is no problem but that does not come throught the speakers either, everthing else in the stereo works perfect, Help