Sonar should block the digital slider of the ChatMix once it detects the headset with physical ChatMix being plugged in. If the digital slider is not grayed out, that means Sonar is still in control of your ChatMix.
This is something that should be resolved by re-selecting your headset in the Playback device via Sonar or by closing the GG software from the System Tray and relaunching it.
You can also try to re-plug your wireless dongle while the Sonar is on. Additionally, please make sure that both your Game and Chat channels have the correct Playback device selected (1) and that you have apps assigned to them in Sonar (2).
Your headset must be selected as a playback device in Sonar, for the physical ChatMix wheel to work. Selecting another device in one or both channels will render the physical ChatMix scroll unusable.
Apps can be moved between channels by dragging, but you will only be able to see the apps that are currently producing sound on your PC.