My speakers are rated at 6 ohms. I first tried the 8 ohm setting on the Cronus Magnum for a few months, then switched to the 4 ohm setting for a month and when I switched back to the 8 ohm setting again, I felt that gave me the best sound. You won't ruin anything by putting the 8 ohm speakers on the 4 ohm taps or vice versa. I got this directly from Rogue Audio. They told me to experiment and what sounded best to MY ears was the best way to go.