The install procedure would roughly be to
- Remove the VolumeGadget from the SideBar
- Close the SideBar completely, by right-clicking its icon in the notification area
- Restart the SideBar
- Install the new VolumeGadget, from http://indev.no/VolumeGadget.gadget
- Open the VolumeGadget settings and define a hotkey for e.g. muting. Save and accept the settings, and try the hotkey.
Also; I've seen that people are requesting multi-speaker configurations. I'll look into that when I find time. In the meantime, if anyone has any suggestions for how that should look / be configured, feel free to leave a comment.