Volume control for Black shark V2

I was under the impression you could control the volume for individual zones using THX and Synapse mixer. If you can, how do you do this? I can't find any documentation and support is very slow in answering. I can slide the dot on the mixer to move it's location but not to increase or decrease volume. My hearing in my right ear is not as good as the left and I need to increase the volume on that side. Any help with this would be appreciated. Thanks...