Editorial Note about the Impedance Selector Switch
I recommend the "Minimum 8-ohms" setting even for 4-ohm speakers of moderate efficiency ( > 89dB SPL). Yamaha includes a" 6-ohm" setting to satisfy UL heat dissipation requirements when driving 4-ohm loads, as well as easing consumer concerns about driving low impedance loads. These switches step down voltage feed to the power sections which can limit dynamics and overall fidelity. My advice is to keep the switch set to "Minimum 8-ohms" regardless of the impedance of your speakers and ensure proper ventilation of the Receiver. To illustrate this point further, I have tabulated my measured differences between the 8-ohm and 6-ohm setting for driving 8-ohm and 4-ohm loads.
8-ohm setting: 134wpc into an 8-ohm load @ 0.1% THD; 210wpc into a 4-ohm load @ 0.1% THD
6-ohm setting: 95wpc into an 8-ohm load @ 0.1% THD; 180wpc into a 4-ohm load @ 0.1% THD