Hi jtk,
In addition to Mojo's correct answer, the advantage of using two 5.25-inch woofer/midranges over one is increased power handling. In other words, the M22 will play cleanly at louder levels (two woofers don't have to work as hard as a single woofer) than a similar speaker with just one mid/woofer. The sensitivity or efficiency also increases somewhat, so it takes fewer watts to produce the same loudness as a single woofer 2-way.
While a traditional 3-way design would be attractive in a small enclosure, it's impossible to achieve greater bass output without considerably increasing the size of the speaker enclosure. If you are doing that, you might as well build a 3-way floorstanding speaker with a much larger enclosure and get much deeper bass extension than is possible in compact cabinet.
Regards,
