The manual is quite clear. See below. Note there isn't a dedicated speaker impedance selector switch. It's a soft switch that controls an input pin on the microprocessor.

https://www.manualslib.com/manual/197545/Yamaha-Rx-V659.html?page=34


v2tov4
A-LFR/1000-8&2,500x2
1000&1500-3
100,160,QS10,800,M2/3/5/50
N2,N3
Audiobytes
A-LFR1500 coming