Hi Snow,
Recent Marantz receivers have had no problems driving the M80s. I'm delighted you like your M80s and I'm sure, as JohnK mentioned, it's very likely a tiny short in your speaker connections.
However, check to see if your Marantz has an impedance switch or a setting in the menu for 4 or 6 ohms or 8 ohms. Contrary to what the owner's manual may indicate, do NOT set the switch for the lower impedance. Leave it at 8 ohms. Setting it lower will limit the power supply voltage and current, which might cause shutdown.
Historically, Denons have had no trouble driving M80s, nor do Harman/Kardon, Sherwood Newcastle, NAD or recent Onkyos.
Regards,
Alan
