Switching between A2DP and I2S audio output

I am converting an older transistor radio into a simple MPD jukebox with a Raspberry Pi Zero W so my dad can play his mp3 collection, For audio output I would like to set the pi zero up as a A2DP bluetooth transmitter to his stereo that has a bluetooth input or through a the Adafruit MAX98357 I2S Class-D Mono Amp to play through the onboard mono speaker.

I have been referencing the Adafruit amp guide and this thread to try to figure out the set-up for both of the ASLA outputs.

I would like to use the original rotary switch to switch between outputs, but I wanted to make sure that would be possible? Can I just monitor a GPIO pin that the switch is connected to and then call “amixer cset numid=XX” based on the switch position?