Speakers and sizes, again.

[UKenGB]

Well, I have some ISO connectors and I was going to make up adapters to connect the Asteroid Smart (how did you know :-) into the original harness. But the ones you show could perhaps save me from having to do that.

What are the wires to the brown ISO connector? Well, I know they should be the spkr. level outputs, but why are these up there by the head unit if the amp is down at the rear? Is it because BMW head units always output spkr. level and higher spec options just boost/process that (in the Rear if fitted) so line level (pre-out) is never transmitted around the car?

In which case, at the back there should either be an amp/booster inserted into the spkr. circuits or if just the basic audio spec, there would just need to be a connector, bridging what would be the in and outputs to and from the amp/booster. I have read somewhere this is how BMW do it and it does make some sense. I just need to determine if that is indeed what they do. Then I will ignore the spkr. connections back to the Rear and install new coax instead. Then connect my amp to the output side of that bridging connector I mention above.

It all comes down to identifying BMW's normal practice with this stuff and confirming that what is in the car matches that. Then I can start installing my stuff. I just don't want to start pulling it apart (and taking the vehicle off the road) before I know what I will be needing to do. I want to minimise the downtime of the car and this sort of research takes a long time so I definitely want to do it all before I start. Hence all the questions that I hope can be answered by those who have already done this. Hope you all don't mind.