I’ve been using C14 since launch and never noticed - but after changing the default value of the audio event it becomes possible to double-click and type in the value.
This is a very exciting moment for me so I am passing it on to anyone else who is trying to fiddle with the little gain control for precise editing.
You can also change the event volume with the mouse wheel, if you enable it in the preferences (Editing->Audio->Use Mouse wheel for Event volume). Which I think is pretty much the quickest way to change the value for a few dB up and down.