I believe the Slice.AudioGain is handled as a per client value today. This means that changes in one client aren't reflected in another. This was done early on when we were attempting to handle the multiple client use case. We have since moved away from that in favor of supporting the primary use case (a single client). If this is a desirable feature to be able to control from other applications, we can change this functionality.
I'm not as sure about the AGCMode. When you say inoperative, what are you trying to do that doesn't seem to work? We actually use that property to set the AGC Mode in SmartSDR.