Welcome!
A difference between the M80s and the M2s? Nah... there's only a 10 driver difference between the two.
Sorry, shouldn't be mean to the new people...(bad Ken, bad Ken!)
In any case, I'm not sure if many people are using H/K 240s with the M80s, but Alan reports good results with an H/K 525 and M80s. The wattage on the receiver will affect how loudly you can play the 80s, but they do have high sensitivity, which means that they can play loudly with little wattage input. In short, I'm not sure. I'd probably edge towards the M60s.
