I used an SDA-4600 amp for awhile with my M2's, but didn't care for the elevated hiss I heard in my system. That in conjunction with the fan noise made me choose the AB class amp route.
I have eliminated the SDEC-3500 fan noise by placing a 200mm pancake fan on top of it. I can't hear it at my listening position which is 4 feet from the unit.
One option for you might be to rent any of the available Pro-Audio amplifiers from your local retailer. It is a very cheap option. It will give you an idea of how much power you require and how much fan noise you are willing to accept.