For Audi cars MMI 2G that don’t have AMI or TV tuner to have audio input, there’s inexpensive device CD Auxiliary optical box to add a CD auxiliary audio input which can be used to stream Bluetooth Audio with smart phones. Quite inexpensive and work perfectly plug and play. All we need is the Bluetooth Audio dongle, RCA auxiliary cable, a ground loop noise filter and the audio from the phones can transmit to MMI audio system.
You can find these on Aliexpress. Make sure they come with optical splitter or it will cost you more money to get one.