Onkyo TX-NR7100 9.2-Channel THX-Certified Network AV Receiver - Manual (Page 106)

106
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.