Back to the A46 internet radio update. In the intervening time, I decided to go the route of removing the tuning capacitor and replace it with a potentiometer, as the tuning mechanism in the radio readily supported that. I had to fabricate a quick and dirty bracket to hold the pot in position, but that was a simple matter of a scrap bit of aluminum and a few minutes work with a bench vise and a hammer. Therapeutic, even..
So, pot in place and tuning dial reassembled, attention turns to the electronics again. I'm a fan of the PIC18F44K22 TQFP44 device as it's easy to solder and has plenty of processing power for what I need it to do - which in this case is pretty much just two things: 1) be an I2C slave to the Raspberry Pi Zero to report position of the tuning, band, and (optional) volume controls and 2) manage the power to the Pi.
Schematic and board are complete, but the board isn't yet constructed nor tested..