Unfortunately the standard itself you have to buy. It's 50 USD for non-AES-members.
ffmpeg -f pulse -i alsa_output.pci-0000_00_1f.3.analog-stereo.monitor -c:a libopus -b:a 128k capture.opus
Sidenote shoutout to PulseAudio. It's really come a long way and things just work nowadays, including high bitrate Bluetooth codecs. I haven't had the need to try something else like Pipewire.
You can (if you are sufficiently well-heeled) use it for home theatre with e.g. a JBL Synthesis 55 and Genelec or Meriden digital speakers.
(Unfortunately, everything in the AV space is fucked up by the copyright cartel, so processors aren't allowed to send anything beyond 24 bit/48 kHz outside their core processing path.)
I still use the SDEC EQ and Blu link for audio distribution in my house.