The Gateway 500S is capable to work as a media player (Gateway music functions are active). In order to turn a main function OFF (media or else), you need to use the DIP switches on the hardware.
There are 6 DIP switches on the bottom of the Gateway. Switches #1-2 are for setting the car configuration (Mercedes, BMW, Audi, Porsche). DIPs #3-4 are not used.
For disabling the media function (Gateway music menu) of the Gateway, you need to turn DIP switch #5 OFF.
DIP switch #6 needs to be turned OFF (in case of the Gateway 500S BT it is for phone). You need to turn this function off, because the Gateway 500S has no Bluetooth functions.
After changing the switches, you need to turn off the whole car with closed doors for 10 minutes to finalize this new setting.