I think what you may be looking for is what I came across a little while ago with a program where I wanted to turn program notifications up, but you can turn it down by setting a lower value then what its at. Its independent of the system volume, however the system value does have SOME impact on the sound volume, so play around with the combinations.
Look <a href="http://www.everythingq.com/forum/moto-q-9h/help-with-imsms-16746.html">here</a>. You should see the registry hack near the bottom.
Play around with it, and see if that helps. I believe it will solve your problems
