SoundSource does not allow different EQ settings to be set for different outputs. It is possible to configure the current EQ settings with a macOS shortcut as described in the manual.
This background daemon will trigger the shortcut automatically whenever the audio output is changed allowing the preferred EQ settings to immediately take effect.
Generate the desired configuration with cmake, compile and install:
cmake -S . -B cmake-build-release
cmake --build cmake-build-release --config Release
sudo cmake --install cmake-build-release --config ReleaseThis installs soundsource-shortcutd to /usr/local/bin and
foo.dill.soundsource-shortcutd.plist to ~/Library/LaunchAgents
Default Configuration
Create a shortcut named Headphone EQ. For example:
Alternative Shortcut Name
An alternative shortcut name can be set in ~/Library/LaunchAgents/foo.dill.soundsource-shortcutd.plist.
Restart the service after modifying the plist with:
launchctl unload ~/Library/LaunchAgents/foo.dill.soundsource-shortcutd.plist
launchctl load ~/Library/LaunchAgents/foo.dill.soundsource-shortcutd.plist