Paul, I think you are talking about something very different now. I too can get Windows sounds, if I only have the device enabled ... Windows just selects it for you ...
How to avoid it ?
Go to the Loudspeaker Icon (Not Minimized hehe) and disable all the sound devices you see (leave the NOS1's be) except for one : the Mobo's sound device (to which nothing is connected). Usually it is called High Definition Audio or something. Now Windows will select that one, and everything will stay quiet because nothing is connected to it.
I know, we tend to shut all off except for our (DAC) sound device, but this is exactly the wrong way because then nothing is left than your DAC to play Windows sounds on ...