Came here with a similar question. Out of curiosity, does OP WorkerOne have a car with Wireless Android Auto? For me, things work properly when I am wired; the car shows up through a Bluetooth connection and presets can be easily saved as normal.
However, when using wireless AA, the car is not picked up as a separate device at all; it merely uses the preset dedicated for the phone speakers, and Poweramp Amplifier reports the "active sound device" as the cars speakers.
I don't know if it's possible to differentiate between "normal" speaker and "wirelessAA" speaker. May be a system limitation. Can apps detect ANY running carplay instance and change accordingly regardless of current output device perhaps?