Hi jesbarmo2,
As others have pointed out on this thread, if you have your Onkyo trying to fill a large room with doors open to a patio, you're likely to run it beyond its capabilities and it could overheat and shut down.
By the way, there is no point in using a resistor in series with a pair of M80s. You'll just waste amplifier power heating up the resistor.
The M60s are an easy 8-ohm load so those would be a good choice. For the big room, M80s would be a better choice, but I'd consider a larger AV receiver from perhaps Denon, with pre-outs for the option of adding a couple of outboard power amplifiers. (Denon receivers have no history of shutting down driving the 4-ohm M80 towers.)
Whichever receiver you use, always run it with the impedance setting at 8 ohms so you don't limit the receiver's output.
Regards,
Alan
