So now the kid is three years old. Sorry for not updating this in so long.
Everything works fine and I ended up scrapping the dual pwm, 16-bit setup because honestly the single pwm, 8-bit setup sounded better. 16-bit sounds much better on a high quality audio player, but in this case it just doesn't. Moreover, the 8-bit circuit and software are simpler. I like simple.
Oh, and here's the software: https://github.com/shlonkin/KeyboardToy