Tim,
2X6 has a point. If the speakers are out of phase, it could produce the effect you describe, as music happening "somewhere down the hall."
While you're at it, check that the gold links between the woofer and tweeter speaker binding posts are secure and connected.
Make sure all the drivers are operating. You can do that for each speaker by using a 9-volt battery and touching the positive and negative leads of each speaker wire to the terminals on the battery while you put your ear close to each driver. You should hear a "click" when you connect the positive and negative leads to the battery terminals (you won't damage a driver by doing this). Do it for each of the six drivers in each M80. If you don't hear a click from each driver, you can assume that something is wrong with the driver or a speaker wire inside the enclosure has come loose.
