Hi! Instead of asking @AnubisZed privately, creating this thread in the hope of helping others and that also others who've faced these issues may chime in...
So I have the newer generation of the AUX version (and having read the forum posts it feels like it’s the worst middle option - it's not documented well-enough as the original version for which Dave's videos are also available, yet not the newest version with MOST fiber optic) - anyway, here’s my attempt to get it working…

I connected the wiring for a test boot up but apparently there’s was a fault somewhere, because the car’s electronics would not turn on at all (after inserting and pressing the key, and/or pressing the engine start button with the foot off the break pedal - no reaction).
Diagnosis:
10pin connector unused?

Can you confirm that the 10pin connectors (male & female) are not to be used and only the 4pin should be used to connect in between the iDrive cable & controller?
(With no instructions to follow, in my installation attempt I connected both - the 4pin to the iDrive and the 10pin to the parking break - seemed obvious at the time - only later I began thinking this may have been a (the?) mistake.)
LVDS cable
Rewatching this section of your original video https://youtu.be/jY-pSPUz0IU?t=633 - can you confirm that the top pink socket on the head unit is for GPS (and the original cable should remain connected), and I should only connect the MMI’s LVDS cables in between the 2nd-from-top yellow socket (and the yellow cable that was originally plugged into that socket)?
(As shown in photo below, for some reason I was connecting the MMI to the top pink connection and puzzled why the green angled connector was turned 90degrees and interfering with the yellow - and why the labels “To OEM Monitor” and “To OEM Radio” seemed switched - I guess this was my 2nd mistake?)

So before I tear the car open again in my friend’s garage, could you please confirm those two mistakes I think I made?
And some additional questions:
In the packaging there was this little thingy which looks like a jumper with some electronic component (a resistor?) that fits this 2wire connector - should that be on or not?


I have two 3,5mm female jacks labeled MIC:
One in the cable bundle with the AUX jack and the camera wires (and the 4- & 10-pin connectors discussed above):

and a second one on the USB loom:

Any idea why - and which one I should connect the microphone to?
And yes, the microphone cable is exactly as described here https://z4-forum.com/forum/viewtopic.php?p=1869483#p1869483 so I’ll be needing to get that Y-loom.
Your instructions suggest using the OEM microphone on the steering column and ditching the one supplied with the MMI - is that because the MMI one is inferior? Would it also be an option to use both - two mics?
Why are there two USB ports? Is it just for convenience - choice of shorter or longer cable - or is there something more to it?
And finally, this is what the jumper setting was when I opened the box: only #5 ON, all the rest OFF. Is that the correct setting?

Oh, one more: I have Comfort Access and have kept the key out of the dash during the first installation attempt, then inserted in for the test. Any special considerations when doing the wiring? Cause I did hear what sounded like various power-related sounds during the deed, so trying not to harm the car
Very grateful for all the help!
So I have the newer generation of the AUX version (and having read the forum posts it feels like it’s the worst middle option - it's not documented well-enough as the original version for which Dave's videos are also available, yet not the newest version with MOST fiber optic) - anyway, here’s my attempt to get it working…

I connected the wiring for a test boot up but apparently there’s was a fault somewhere, because the car’s electronics would not turn on at all (after inserting and pressing the key, and/or pressing the engine start button with the foot off the break pedal - no reaction).
Diagnosis:
10pin connector unused?

Can you confirm that the 10pin connectors (male & female) are not to be used and only the 4pin should be used to connect in between the iDrive cable & controller?
(With no instructions to follow, in my installation attempt I connected both - the 4pin to the iDrive and the 10pin to the parking break - seemed obvious at the time - only later I began thinking this may have been a (the?) mistake.)
LVDS cable
Rewatching this section of your original video https://youtu.be/jY-pSPUz0IU?t=633 - can you confirm that the top pink socket on the head unit is for GPS (and the original cable should remain connected), and I should only connect the MMI’s LVDS cables in between the 2nd-from-top yellow socket (and the yellow cable that was originally plugged into that socket)?
(As shown in photo below, for some reason I was connecting the MMI to the top pink connection and puzzled why the green angled connector was turned 90degrees and interfering with the yellow - and why the labels “To OEM Monitor” and “To OEM Radio” seemed switched - I guess this was my 2nd mistake?)

So before I tear the car open again in my friend’s garage, could you please confirm those two mistakes I think I made?
And some additional questions:
In the packaging there was this little thingy which looks like a jumper with some electronic component (a resistor?) that fits this 2wire connector - should that be on or not?


I have two 3,5mm female jacks labeled MIC:
One in the cable bundle with the AUX jack and the camera wires (and the 4- & 10-pin connectors discussed above):

and a second one on the USB loom:

Any idea why - and which one I should connect the microphone to?
And yes, the microphone cable is exactly as described here https://z4-forum.com/forum/viewtopic.php?p=1869483#p1869483 so I’ll be needing to get that Y-loom.
Your instructions suggest using the OEM microphone on the steering column and ditching the one supplied with the MMI - is that because the MMI one is inferior? Would it also be an option to use both - two mics?
Why are there two USB ports? Is it just for convenience - choice of shorter or longer cable - or is there something more to it?
And finally, this is what the jumper setting was when I opened the box: only #5 ON, all the rest OFF. Is that the correct setting?

Oh, one more: I have Comfort Access and have kept the key out of the dash during the first installation attempt, then inserted in for the test. Any special considerations when doing the wiring? Cause I did hear what sounded like various power-related sounds during the deed, so trying not to harm the car

Very grateful for all the help!