After reading your post, it sounds like you have done a lot of research and know what you are doing- but to sum up my thoughts... It would be very sad if you didn't get the M60s and the 500. It is the better system.
Using 2 smaller subs (dealing with levels and phase issues) can make it more difficult to get things sounding right, and you wouldn't get the performance in output and extension you would with the EP500.
I would think that you will find the M60s and the EP500 with a crossover of 60 Hz should blend very well, and not be a problem. But I certainly can't say for sure as every situation is different. I would reccomend you go this route, and even start with the M60s set to small for movies with 80Hz crossover, and then move to 60 and see which you prefer.
Best of luck. I'm sure others will give you some additional advice. Welcome too.
