Hi @L05T, is it the 2nd generation RNSE, with the Media button? To get the distance image (Audi Parking Plus) on the screen I believe you also need front sensors then the coding updated - this is what I had to do on my previous A3.
Re the volume, if you can't change it via the RNSE (may need the above) then you should be able to change the volume via the DIS switch.