Eric, welcome. As to getting the M60s and then wishing that you got the M80s, if that's your philosophy about whenever there's something available that's even slightly better, then yes, that's what will happen in this case. The M60s should serve you well for many years, on the other hand, if the itch doesn't get to you.
As to the 4ohm setting on the receiver, disregard what the manual says and keep it at 8ohms regardless of what the impedance rating of the speakers you use happens to be. The 4ohm setting is simply a type of safety precaution to keep the Underwriters Lab happy because it helps reduce the chance of overheating.It does this by reducing the maximum voltage that the receiver's power supply section can output, and because of Ohm's Law, when the maximum voltage is reduced so is the maximum current and power available. So, although the chance of overheating is reduced, so is the maximum power that would be available otherwise(as much as 50%).
