It looks like that project is a synthesizer to generate sounds rather than to play WAV files. I didn't read everything, is there a DAC for getting analog?
I'm wondering what way I can wire this to play simple WAV files,
sound quality is not important, I just need to hear it working.
You can not use this wiring. You need at least a filter between the Arduino and the speaker.You or whoever set the assignment?
OK for fun then look at this link:-https://github.com/TMRh20/TMRpcmQuality crap but hey it does some sort of job.