I'm designing a new system for a 1200sq ft loft in L.A.. A subwoofer is not in the plans but I would like to still be able to achieve low enough base to give some punch to music and movies. The owner of the loft isn't the bass nut that most of us probably are and would be bothered by very deep bass at high SPL's. Anyway I'm debating over M60's and M80's as mains. If I go with the 60's I feel comfortable driving them with a Yamaha RX-V2600. However, I'm not sure the amp would handle the M80's as well (4ohms). Any thoughts or suggestions? I have been looking at the Rotel amps for this. I'm thinking a 2 channel amp between 120-200 watts/channel at 8ohms (300watts @ 4ohms = RB1080) should be sufficient.

SoCal I'm not familiar with the Yamaha receivers so therefore I'll sidestep that side of the question.
The Rotel 1080 is very sufficient for driving the 80s. I have a 1080 connected to the preouts on an H/K receiver driving a pair of 80s for the mains and use the receiver to drive the center and surrounds. Works great.
Check out this thread from the Audioholics site, there may be some useful information in there for you.

If you can afford Rotel RB-1080 go for it! I have it with M60s in a stereo setup, and even though M60s are very easy to drive speakers, more power does not hurt. And of course, 1080 will serve more than well if you decide to get M80s.

SC, judging from the reports on the 2500, the 2600 should be fine with both the M60s and M80s unless the listening level would be extraordinarily high.

I don't think you'll need one. but the amp let's your 80's bring down the house.

My 3805 was running the M80's fine. But another Amp improved things and added a little bit more headroom. To my ears, my system sounded sweeter after adding another Amp.

in a large room with the 80's, I would consider getting an external amp for the 2600 or at least move up to the 4600 if you don't need HDMI upconversion. You would be better off with the 2600 as a pre and a rotel amp for sure. The amps on the yamaha won't compare to the Rotel.

That being said, by the sounds of it...no pun intended, you don't want to have it that loud anyways, so maybe you will get away with the 2600 on the 80's but to be honest, what you find "loud" and what I find "loud" could be entirely different. I'm in a 11x17 room, and the 4600 powering my setup has more then I'll need. But I don't exactly listen to things at 90db either.I'm more about quality then just plain loud.

I don't think the 60's would be an issue either which way. The only question is...will you wish you had gotten the 80's in the 1st place? If you can resist that temptation, get the 60's, save some money on amps and speakers.