The newer arduino's come with a pretty powerful IC for the usb interface. So I reflashed that using LUFA. To be clear the audio quality was awful, but could certainly hear what was playing. Here is the repo for it. I did it as a self directed class in university. Treat it like I had no idea what I was doing trying to understand lower level programming! https://github.com/ElementalWarrior/ArduinoAudio (This was in C, not part of the Arduino ecosystem with the IDE)

Interfaced with an FTDI chip maybe?