Perfect for a headless Plexamp pi feeding a Genelec SAM system! :-)
The missing star is for lack of documentation and a little for lack of a suitable case. Stole the idea to use a low profile passive heatsink case from Geekworm and cannibalize their acrylic plate "case" for a hood and bits, Works, but the hat still remains pretty exposed.
What's actually needed to get it working: 'dtoverlay=hifiberry-digi'.
Can't figure out (with enough certainty, not going to guess) where/how to wire a coax S/PDIF output; Really should be documented here.