Just tested on a clean windows installation. No it doesn't work. You see, on a clean windows installation, [HKEY_CURRENT_USER\Software\Microsoft\Multimedia\Sound Mapper] and [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Multimedia\MIDIMap] doesn't exists. If i set only the "PreferredOnly" value, windows does not create the other values ("Playback", "Record" etc) On a machine that has already checked the checkbox, your registry value works fine ("PreferredOnly"=1, enabled - "PreferredOnly"=0, disabled) Thanks for your time.