Onkyo TX-NR6100 Instruction Manual page 102

Playback
• If "On (A+B)" is selected as an audio output destination, you can select only
the "Stereo" listening mode for ZONE A when using the 2.1 ch speaker layout.
When using a speaker layout of 3.1 ch or more, you can select only the "AllCh
Stereo" listening mode.
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