GAME/CHAT/MEDIA/AUX virtual mixers in Sonar cannot be selected directly within the Sonar mixer as they are not physical devices.
Instead, the virtual devices populate within Windows and other audio settings, such as your in-game audio configurations. Only physical audio devices detected within Sonar can be selected within the mixers.
When adjusting the mixer settings, changes apply to the specific mix associated with the output device specified in Windows audio settings (e.g., GAME, CHAT, etc)
GLHF!