Hmmm..
Nice write up! I have seen you respond to other members in the past…You defiantly have an excellent technical background and great writing skills!
Electronics is my occupation, however audio stuff is something I never paid attention too. Passive filters are universal apply to more than audio.. so thankfully I do understand what I’m looking at.
Anyway It occurred to me today that the crossover section is too important to loose. After reading your post, I think I’ll toss the idea of building a bypass harness and try and salvage the crossover section.
I like your idea of pitching the OE power section and utilizing the crossover with a high power amp.
My OE amp has the power transistors and the crossover components mounted to the main circuit board. There are two little circuit boards mounted at right angle to the main circuit board. Each board has a single 20 pin DIP M5243P12. A quick check on the net says this chip is a tone control three- element EQ. No data sheet were found. Perhaps these little boards are tuned to the particular cabin?? Hard to say at this point.
The amp has two 12 pin connectors. One black and one white. The part number is 65.12-8 350 407.
It sounds like you have experience in hacking the BMW OE amps. It sounds like mine is closer to the 535 description you gave.. or did I misread that?
Am I in the right direction or did I miss something?