I own M22;s and will very soon be bringing them back into my life (they're currently boxed up as we are two people living in a 240 sq feet apartment with thin walls).
I love them, even on their own. Yes, the bass is 'weak' compared to a speaker that has, say, a seperate woofer. But it's tight and rolls off very, very well. I was in fact a little surprised at how much bass they give consdering the 5 1/4 inch woofers. A sub is recommended, but not absolutely necessary for most music.
The M22's have such a wonderful soundstage and are so clean and clear you can't go wrong.
