Updated example code here:
https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview

Includes:

- Optional IIS/Analog input based on commenting/uncommenting the global variables to set up IIS or analog audio routing.

- Some additional work done on attempting better "initial connection" experience and play/pause behavior at start of the car.

- Some other tweaks, I forget them all at this point. :-)

Next goal: modifying the wires on the tuner connector to carry the IIS signals instead of the tuner signals.