Marantz SR5009 Owner's Manual page 188

Contents Connections
Front Speaker
Set the front speaker A/B to use for every sound mode.
A
Front speaker A is used.
(Default):
B : Front speaker B is used.
A+B : Both front speakers A and B are used.
This can be set when "Assign Mode" is set to "Front B". (v p. 181)
Front panel Display
Playback Settings
Rear panel 188
Tips
Remote Index
Appendix