Wow, huge price difference in purchasing abroad vs via Crutichfield (though I never buy through CF). I have no concerns with buying abroad other than the tariffs (10-15% as of late vs 0% before last year).
I've read a lot of your posts and you always provide solid advice, so I knew you'd come through again on this. I agree with you that factory drivers are often 'okay' but rarely great. I replaced the stock drivers and tweeters in my last BMW and that made a nice improvement, but as you said, the big difference came when I upgraded to a DSP amp (Audiotec-Fischer Match Up 8).
Have you found a drop-in replacement for the sub driver? I'd personally rather just disconnect it and use a compact sealed enclosure, but then Ill be getting into needing to power it which opens the amplification can of worms sooner than I'd like to. Or can the ML amp power a sub in a sealed enclosure?
My initial thought based on your advice was to go headless, but for the sake of my family, I think I'd like to have CarPlay capabilities. To that end, I came across a thread of someone who ran the output of his Teyes headunit to the optical Input of his DSP amp (an Alpine Omega 8) with excellent results, so I'm now considering either going the Teyes route to retain AC controls and a nice integrated look OR waiting till the hardware HVAC control module is available and then getting with a floating 10" screen from one of the reputible headunit manufacturers (though the Teyes still wins on how 'factory' it looks in the dash).
I'll contact you offline regarding the adapters, both for drivers as well as for the tweeters.