From Stack of Boards to Boombox (with Up2Stream Amp 2.1)

Just a quick update since there was no reply.

I tested the ADC_Key without the 0.1µF cap in the diagram on a breadboard and it worked for me on U2S AMP2.1. I then added it to my DIY button board and it works there, too. That is for the buttons I am using: Mode, Volume -, Volume +, Mute