I recently purchased a Sont ES reciever to go with my Axiom speakers. Sony says if any one speaker is less than 8 ohms to use the 4 ohm setting. I have four M60s (8 ohms) and a VP150 center(6 ohms) so I set the receiver on 4 ohms. Is this the best way to set the receiver? What is the advantage or disadvantage of using the 8 ohm setting vs the 4 ohm setting????