On each LISY MPU you find a place für inserting an (optional) pHAT compatible soundcard. I build my own soundcard by using standard components you can find for example on eBay or Aliexpress. Gerber Data to produce you PCB you will find below.
By using my PCB and the listed components you can have this for less then 10 Euro, a similar Commercial card ( HiFiBerry MiniAMP ) is about 20 Euro.
Gerber Data is for Version 1.2, which has some small corrections