The 4 ohm setting will merely current limit, which is actually a pretty bad thing as far as the speakers and your use of them is concerned. Choose a different brand. I run my M80s off of an H/K 525, but I have a small room and modest listening habits. Others have found that they need external amps with M80s to achieve the volume levels they want.

If you're dead set on the Sony, get M60s.

I am the Doctor, and THIS... is my SPOON!