a-them AVM 90 Operating Manual page 34

Subwoofer / Center / Surround / Etcetera
Anthem Room Correction automatically sets these.
For manual setup, if you are using any of these speakers, set each to "On." Otherwise, set them to "Off." This step is
essential to keep sounds from going missing. Setting unavailable channels to "Off" causes sound (that would
otherwise have come from those speakers) to reroute to the appropriate available speakers. Front speakers cannot be
turned off, these are required for all profiles.