Hang on, do you mean you can connect your phone to the Mr12volt and play music through your cars speakers without seeing the Mr12volt screen being displayed??!!
If that is correct then I'm wondering if you've, somehow, connected the LVDS wrong (not sure how off the top of my head though).
So with the new two into one LVDS cable now being used, one end is Female and one is Male. The Male end goes into the rear of the headunit, and the Female connects with what is the original Male that was removed from the headunit, this original goes directly to the screen.
Also, sorry when I said about plugging a memory stick into the USB, I meant the OE USB in the centre console, not the one for the Mr12volt.
An explanation - If you have the amplified Business system then this is connected via speaker wires from the headunit to the amplifier.
With the Professional amplified system this uses the fibre optic from the headunit to the amplifier.
Your Bluetooth, USB, AUX are connected to either a Combox (Bluetooth audio & calls) or a MULF (Bluetooth calls only), these are both connected via the fibre optic network.
If you have a break or cross anywhere within the fibre optic network then none of these will work, ie; Bluetooth, USB, AUX and Amplification with the Professional system. If you have the Business system then you'll still be able to have audio from the radio only, but nothing else will work, not even show as available (ie; twirling Bluetooth, no USB available etc), hence why I was asking, and specifically the OE Bluetooth and USB. My thought was that you still have an issue with the fibre optic network somewhere.