In case you are interested, I have a 3D printed case design on thingiverse.com: https://www.thingiverse.com/thing:2813477. The Pi Zero is powered by Volumio. This makes a nice, small box that you can either listen to on headphones or attach speakers to (haven’t tried that, likely they need to be powered!). I built Volumio on a 128GB micro SD card, so I can have a sizable music library to listen to by using the “host-apd” option of Volumio and managing playback with your phone/tablet.