JP, if it's a problem it should be no more than a very minor one. 80Hz is the most commonly suggested crossover, which isn't something picked randomly, but was determined to be a good compromise, being high enough to take some of the low bass burden off the mains(and on to the sub which is designed to handle it)and low enough so that the sub shouldn't be localizable. 100Hz is close enough so that there shouldn't be much of a problem, especially if the sub is placed in a corner more or less directly behind an M2. You should use the receiver crossover rather than the one on the sub's outputs, since that's frequently inaccurate. Turn the sub crossover control all the way up to get it as far out of the way as possible if the sub doesn't have a switch or input which totally bypasses its crossover.
