OK, it seems your 6M extension cable is quite different than the one Xtrons uses. Can you confirm that that 6M cable has 4 BMW connectors at one end and a single connector at the other end that connects to the Eonon head unit?

What's confusing me is that they show a "normal extension harness" and they also show the 6M harness without clear indication as to when each is used.


Have a read of https://www.m5board.com/threads/help-eonon-ga6201-android-headunit-a0579-harness.554561/#post-7247169 - sounds similar to what you're experiencing. Although it's not exactly a config you can drive around with try reconnecting the old BMW headunit at the two BMW connectors in the dash while leaving everything else connected and see if you get sound? If yes I think you need the Resler ibus interface and the app on the radio to tell the DSP amp to turn on. Or find a hardwire way to achieve the same. I have also see a mention of "You must Recode your DSP amp using NCS Expert. Change the BEDIENELEMENTE parameter from “bordmonitor” to “mid_basis"