Your V2600 will have no problem driving the M80's. No doubt though the M80s will put more load on the amp than the M60s will.
I remember my first Yamaha receiver from more than 20 years ago. In the comment area of the registration card I mentioned that perhaps the receiver needed a cooling fan. Heat is nothing new to Yamaha receivers; they simply run hot. I would never place a Yamaha receiver in an enclosure.
In the setup menu, you can set the cooling fan to continuous. The receiver's protection circuits will shut the receiver down if it gets too warm. If this happens frequently then set the fan to continuous.
I have the Yamaha HTR-5990 and it runs rather warm like the rest of the Yamahas, but I have not had to run the fan, even after 8 or 10 hours of combination movies and 2-channel stereo listening. If the fan has come on, I've not heard it do so. One feature mine has, and yours probably does too, is Pure Direct, where all features of the receiver are shut down (video circuitry/processing namely) except for 2-channel or multi-channel audio...even the display goes to sleep. I've noticed the receiver runs cooler if this mode is used when listening to audio only.
Even with the heat, I'm sure you're enjoying your Yamaha as much as I enjoy mine.
Regards
