Investigating wiring to speakers

[CamelX]

As the car had a replacement Android head unit in the ATH20 that wasn't working, I proceeded to swap it for one I had with carplay and looked around to see how it tapped into the speakers. Based on the info from this forum, I counted 17 speakers and a subwoofer under the drivers seat. I see the android head unit plug containing the speaker lines connected to a brown connector which I assume is part of a bypass cable leading to the area under the passenger seat. I haven't gone around testing what speakers emit sound although I have read the subwoofer is not used. 

 

I'm curious how the 18 speakers were used in the oem and whether the subwoofer can be reused or connected to the subwoofer output of the Android headunit. I see aliexpress sell large head units. Would these use the full 18 speakers?

[CamelX]

More investigation.. Piecing together the capability of this car and I suspect it has a screen mounted on the roof. I can't be sure as its flush and may just be a blanking plate. I'll try and post an image.