Hi Laurie,
While I'd agree in principle with JC on amplifiers using MOSFET output transistors (nothing to do with tubes, by the way), it's not the only way to design a robust amplifier.
Given the room dimensions, I'd suggest you go with the Denon 3806. The Denons are powerful and do not shut down with lower impedances such as the 4-ohm M80s. Generally speaking, they have more robust amplifier sections than the Yamaha's and Pioneers, although several models from each of those are very good.
While your M60s are 8 ohms and an easy load for any AV receiver, I'd still opt for the Denon because of my comments above.
