Okay. You have 5 actual speakers.
In 5Ch mode, everything works great.
The issue is only with the 9CH VIRTUAL DSP mode, which uses DSP to create the other 4 Virtual speakers.
So the culprit is the lousy DSP modes (specifically the 9CH Virtual DSP Mode),which is why most of us hate DSP.
I wish Yamaha would get rid these million DSP modes that belong in Karaoke machines.