I don't own the M22s, but I use the foam plugs on my MA GR 10s. In my room it really cuts down the boominess and tightens it up considerably. The downside is I lose a bit of the visceral impact of the bass. Just makes me want to turn it up more! Without the plug the bass tends to overwhelm the music and drown out the other notes. I think it really depends on placement and room acoustics.

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"Nothin' up my sleeve. . ." --Bullwinkle J. Moose