radtek2,
Ask Onkyo if the 797 will deliver its FULL POWER OUTPUT into a 4-ohm load with the switch at the 4-ohm setting. I'm fairly sure that Onkyos of the 797 vintage inserted a current-limiting circuit at the 4-ohm setting to prevent the output stage from overheating. But it does that by limiting the power output to about 30 watts per channel. And if you get the M80s, you are going to want a lot more power. If Onkyo says, "Sure it will drive 4 ohms." You should say, "Yes, but what is the maximum power output into 4 ohms with the switch at the 4-ohm setting?"
Regards,
