I've remapped my F10 and F12 keys successfully to be volume mute, volume up respectively. When I try to remap F11 to volume down, it recognizes that I pressed F11 and populates the "(hot key) is pressed" field with "F11 is pressed" but performs the default system option (Mac, clear desktop or something) instead of turning down the volume outside of feeding it that input (ie actually trying to adjust the volume). If I map volume down to F10, it works fine.
Since the others remapped okay, I expect this is a problem specifically with the F11 button and/or my system. Any ideas? Thanks!
Hot Keys do not override other application or system hot keys. All applications that register interest in a hot key will be alerted to the pressed hot key. The key is swallowed so that the current application will not see it as a normal key, but each application (including the system) will be notified of the hot key press.
So you will need to find a way to disable the F11 behaviour - usually for the system these are configured in the System Preferences, Keyboard, Shortcuts.