Because applications change and are in the few thousands now, it is easy to see why no such volume control app is feasible. I see you can control the Windows sound system but little else can be expected today.
Your post reminds me why I like my old desktop at times where the volume control knob was easy to use and worked over all apps and more.
I am looking for a program that would allow me to adjust the volume of different applications (and master) using hotkeys (+mouse wheel) in Windows XP.
A few programs come close, but either don't have application control or don't support hotkeys.
If anybody knows of such a program please share,