There are a lot of existing Audio Setups for the Raspberry Pi. Yet I always seem to find something, that existing solutions are lacking for my personal usecase. Here are some of my setups . Often to special to make it into a mainstream solution; hence Niche Audio.
PiCorePlayer An easy way to a great music experience.
A Toniebox(R) like RFID Player for adults.
Setting up the Hifiberry DSP on picoreplayer