Aaron no, the manual said what was intended: for 4,5,6 or 7 ohm speakers set it to 4 ohms. However, ignore that and leave it at 8 ohms except as a last resort if protection circuitry was shutting off the receiver. When 4 ohms is set it limits the voltage and therefore the maximum power that can be supplied, so this should be avoided if possible

M60s should be plenty for you.

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Enjoy the music, not the equipment.