The Mercedes-Benz MMI CarPlay box can transfer the sound through OEM Bluetooth (instead of AUX), that way, it can improve the sound quality of CarPlay.
To make it work, first to update the software to v3.6.0.14xxx version, then go to the setting interface, turn on "Use Car BT channel", after that, connect your phone to CarPlay (or Android Auto) and OEM Bluetooth simultaneously！
Please read below guide in details.
Q1: What kind of model can be upgraded?
RE: The NTG 4.5/4.7/5.0 with OEM Bluetooth Audio.
Some Mercedes NTG 4.5 cars also have "telephone" function and can connect to the cellphone, but if the model don't have "Bluetooth music", It also not support.
The Mercedes NTG 5.0 have OEM Bluetooth and Bluetooth audio.
Q2 How to download and upgrade the software?
Which version should I need?
(1) For now, the version : v3.6.0.14 xxx support this function.
(2) The software as below, please download the right version for your model:
NTG 4.5
Version: lybenz2_3client-v3.6.0.14.ly.m4_2
Download
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NTG 5.0
Version: lybenz52_3client-v3.6.0.14.ly.m5_2
Download
(3) Which version for my car?
Access to your CarPlay menu and check the software version first.
For exmaple, below photo is the software version from a Mercedes Carplay box.
You can read the "Custom version", it have "m5_2" in the end, that means: you should use NTG5.0 version, so, you just download and update lybenz52_3client-v3.6.0.14.ly.m5_2, then will be fine.
(4) Do I need to upgrade the MCU or other software?
No, don't need it, just upgrade the software mentioned above only, the MCU keep it same as original.
Q3：How to update the software?
(1) Prepare a U-disk(USB drive), better less than 8GB, format FAT32
(2) Download the software, you need to decompress the zip file(unzip the file),
will see two files inside (GEMINI_PACK.BIN & ISPBOOOT.BIN), copy this two files, to the root of USB drive.
(3) Connect the U-disk to USB of MMI Carplay BOX.
(4) Go to Carplay box menu: click "setup"/software update/ input the password 2916 / click "system update"/ it pop up a "User update via USB", click "V" to confirm it/ it will update automatically.
Notice: Don't power off the car during update, you should keep car engine power on, it will take few minutes for the update. After it finish the update , it pop up "burn success,welcome", it will restart the unit automatically, after that, you can remove the USB drive.
(5) After update, you can go to "Setup"/software version, to check if the version changed or not.
Q4: How to make the settings?
Go to "setup" , and turn on " Use Car BT channel", and connect the phone to Carplay (or Android Auto), also connect the phone to OEM Bluetooth at the same time, you will access to original interface, choose "multimedia/external device/ choose "Bluetooth" (instead of AUX). Then will be fine.
Note: After audio transfer via Bluetooth, when you use USB drive or Airplay to play the music, the audio will not work. You have to change the setting (set off the "Use Car BT Channel", and choose "AUX" in original interface, only that, the USB drive & Airplay can work.