Toggle mute system volume - Toggling by MiddleClick on Speaker icon in Tray

You can do that if you enable one of the volume wheel scroll options.

Nice.

Unfortunately, I decided not use those "volume wheel scroll options", because WIndows unmuting the volume when scrolling by mistake. It is not the behaviour I want.
To get over this problem I'm using HotkeyP volume commands. It doesn't Mute/UnMute automatically, but by a command.
I would glad to see what I suggested in OptionsEx.

The feature was implemented as a part of the Mouse Button Control advanced options in v5.1.0.6 beta, with greater flexibility. Please try it.