There really isn't much benefit to having double the speakers. There would be no gain in quality, unless m80's sound better at lower volumes for some reason (hence the combination of two at the same level would sound better). You could actually hinder some aspects of quality depending on placement. The amount of added spl would be minimal with only a 3 dB increase which is close to the threshold of a noticable difference in level. A doubling of sound pressure generates a 3 dB increase in level.