Pipewire is a replacement for both Jack as Pulseaudio. Because it is ABI compatible with JACK2 the Jack version of Stereotool has issues. This causes the inability to connect to the substitute jack server for Pipewire, and worse: crashing stereotool for eating up all real time resources.
We will first introduce a source/sink pair.
pactl load-module module-null-sink media.class=Audio/Duplex sink_name=my-tunnel audio.position=FL,FR,RL,RR
Download the ALSA version of PulseAudio. For Input use pipewire (ALSA). For Output use pipewire (ALSA).
Now we connect stereotool.
pw-link "my-tunnel:capture_FL" "PipeWire ALSA [stereo_tool_gui_64]:input_FL"
pw-link "my-tunnel:capture_FR" "PipeWire ALSA [stereo_tool_gui_64]:input_FR"
Now you can play a sound via the tunnel via:
mpv --audio-device=pulse/my-tunnel 03.\ Taylor\ Swift\ -\ Style.flac