I tried to edit my xfce4-panel.xml and the following line: <property name="volume-step" type="uint" value="3"/> To set the volume step to a lower value. I tried to insert this line while xfce4-panel was running, and when it was not. Nothing works, the setting is removed every time the panel is restarted.
Try using xfconf-query with a command like: xfconf-query -c xfce4-panel -p /plugins/plugin-18/volume-step --create -t int -s 3 Change "plugin-18" to the actual plugin value. For more info, see: https://forum.xfce.org/viewtopic.php?id=12082
Thanks. I think some documentation about hidden settings is missing. Or I missed it myself.