Which mouser/digikey(...) product code should I order to solder a Line Out connector in the 5-holes Audio board space?
First, let's make sure we're talking about the same audio board. This one, right?
https://www.pjrc.com/store/pt8211_kit.html
Digikey CP1-3525N-ND works. So do many others.
Here's a link to a writeup I put on OSH Park with more info:
https://www.oshpark.com/shared_projects/TyqlhCdw