Marantz SR5009 - Manual (Page 195)

Front Speaker
Set the front speaker A/B to use for every sound mode.
A
(Default):
Front speaker A is used.
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. 188)
Contents Connections Playback Settings Tips Appendix
195 Front panel Display Rear panel Remote Index