I have listened to a few of the MA speakers and I'm willing to bet they sound very similar with the 500's giving slightly more bass whole 2hrz worth. I've not heard the 500's so i'm speculating but from what my dealer says they are almost identical with the 500 adding a smigit more bass. so go listen and see.
If you don't need the bass you may want to consider moving up to the monitors in the gold line for the same money much improved IMO.