Reiterating, but I'm really happy with my solution:
I just can't think of a reason to have system sounds. Or, if you really like them, it isn't much work to switch on/off during FOF play.
By the way, the shortcut for the volume control is this: %windir%\System32\SndVol.exe
If you need a quicker way to bring it up than finding it in the systray on the taskbar.