Minor ebuild dependency issue ... media-libs/libao with USE="pulseaudio" flag enabled should depends on media-libs/libpulse and not media-sound/pulseaudio
I found that whilst migrating from media-sound/pulseaudio (that doesn't not work well detecting Bluetooth headset since version 16) to media-video/pipewire.
libao just compile fine with libpulse w/o neither pulseaudio or pulseaudio-deamon installed.
Tested with media-sound/pianobar (which have libao as dependency). Sound OK for Bluetooth headset & speaker with pipewire as sound server.