I have a whole house system with a ZPR and SmartPad3's. Everything works great except I haven't found a way to shut a source off when there are no zones no longer using it. I control "on" with a discrete code. I would have thought the ZPR would "know" when a source is no longer being used and be able to issue an "off" after the last zone that is using it. Is there any simple way to do this (without buying an audio sensing device)?