Strange Stereo Wiring - 2004 BMW X3 Pics Inside

Hello everyone, I am trying to install an aftermarket head unit in a 2004 X3 manual transmission (LHD U.S. model), and am really stumped with this. I've done plenty of installs before but this is really not making sense to me. According to all the pin-outs and pictures I've found online, this is basically how the car side is supposed to be arranged: But this one is different; namely, it is missing [what are supposed to be] the rear right and rear left outputs, both positive and negative. What is has are ostensibly the front left and front right outputs, two colored brown/orange stripe, one colored blue/red stripe, and one colored yellow/red stripe. Putting aside the fact that these colors don't match up with anything I've seen online, I'm supposedly missing four other wires on the top and bottom of that set of pins! I've also pulled the rear Lear amplifier out (42 pin) and examined the wires, and it seems to have four-channels of input coming to it (8 wires) as well as a host of wires coming out. The stock stereo works perfectly, fade, balance, equalizers, everything works. But when the aftermarket unit is installed with the Crutchfield adapter, it-predictably-doesn't work. It turns on fine, but no sound with any input. I've scoured the internet and I cannot find anyone mentioning this problem. As I see it, it seems that there has to be some splitter between the deck and the amplifier that I don't know about. Any help would be greatly appreciated.

Ugh, guess I should have searched just a bit more. Turns out that the car has a "high-end" Carver DSP system which takes the two channels and splits them among all speakers. The stock head unit has a K-bus out that is what essentially makes the whole thing work. My research indicated that people went one of two routes - chucked all the factory equipment and replaced the entire system, or set the stock head unit as a "dummy" in the trunk or in the glovebox, with it hooked up to power and the K-bus. The aftermarket stereo can be installed with the Crutchfield/Metra adapter as normal. Being that the factory unit could not fit in the glovebox, I put it in the trunk and ran a wire from it to the K-bus wire at the head unit. It's just set up as a proof of concept right now, but it works excellent. You can read more about this here: [url]https://www.bimmerforums.com/forum/showthread.php?2096893-DIY-Aftermarket-HU-in-2001-540i-w-DSP[/url] That's a fantastic write-up. There's also a nice video here: [url]https://www.youtube.com/watch?v=34c0uaoLrdc&t=462s[/url] It seems to me that this method can be applied to a wide range of years and models, but beware that there are some differences and you should look at the above guides as references, and expect that your car might have some differences, certainly with amp connectors and the like.