The volume control pictured is a dirty hack perpetrated by a banned component. I call this a dirty hack because:
- The volume control subclasses the UI window to insert the volume control into the toolbar. This will only work with specific UI components which behave exactly as the author expects, and will break any time the UI dialogs happen to change. This is not within the scope of the component API, and is why the component is banned.
- The author used a progress control instead of a slider control. Sure, with slider, you have to monitor clicks anyway if you want it to jump to exactly where the cursor is clicked instead of stepping there gradually, but it still looks strange.
I discussed the matter of porting the component to a UI Extension with its author. I'll refer him to musicmusic's example components and see how that goes, but unless he eliminates the subclassing completely, it will remain banned.
You could always wait until someone else writes a UI Extension which controls either the system mixer or the internal volume control DSP.