The key here is: bus architecture. A number of different protocols and buses are implemented in order to transport the different signals to the different units.
For video signals, for example, GVIF (Gigabit Video Interface) is a very typical copper based bus; for audio we are talking MOST (Media Oriented System Transport), a plastic optic fiber bus in a ring fashion.
Usually a single CAN (or FlexRay) connection is used between the infotainment and the powertrain, in order to gather information about the vehicle or send some commands (4x4 mode selection for example).
There are mainly four units in such a setup:
- Dash screen, usually pretty dumb and only dedicated to HMI;
- Basis infotainment unit, usually the same along the whole vehicle portfolio. Navigation, connectivity and vehicle interface run here;
- Rear seats entertainment unit, usually offered as an attachment to the main unit, in order to extend the functionality to the rear seats and let them work independently;
- Audio amplifier. Usually separated from the rest and driven through a digital interface, such as MOST or even SPDIF.
Many accessory units can be attached to the system, such as DVD players and even a Playstation. Vintage analogue signals, sich as CINCH stereo and composite are not rare here.
In my experience, 36 speakers only lead to an increase of the fault probability. I had enough issues with my 12 speakers setup, when only 4 would abundantly suffice.