Shairport-sync looks to be similar to net-libs/shairplay, but it worked perfectly out of the box (which shairplay does not) and supports the newer synchronized audio mode in AirPort. It'd be great to have an ebuild for it. Reproducible: Always Installing in my homedir worked fine, via: ./configure --with-pa --with-avahi --with-libdaemon --with-ssl=openssl --sysconfdir=$HOME/local/shairport-sync/etc --prefix=$HOME/local/shairport-sync make install
https://repology.org/project/shairport-sync/versions
I'm using it too, so I create a ebuild for it: media-sound/shairport-sync in griffon_overlay. Also add alac library, hope this can help.