Guess you are trying to play music on lap onto car speaker system?
If you have a newer E46 (~03) there is an aux option you can purchase from BMW. If earlier model best way is to emulate CD changer and use that audio input. If you do not emulate CD changer the head unit will not let you select CD changer. This is done on IBus as you are aware.
About AV input (you want PC screen on bordmonitor?) you have to change VGA to RGsB and then input it in the VideoModule were the revers camera normally is connected.
But to be honest, your question does not make a lot of sense to me :-)
Lots of info on HackTheIBus yahoo group and you seems to have found carx.
Sorry, I was assuming you've got a business system. DSP system is different