The bulk of musical instrument harmonic content lies in the midrange, where, incidentally, human hearing is also the most sensitive. Speakers like the M22s that have lots of midrange detail means you'll hear the pluck of acoustic guitar strings, the sibilants of singers' "sss" and "ttt" sounds (those can be exaggerated if the original CD has been goosed in the mids for airplay)---more detailed speakers also tend to have a greater sense of spaciousness with live or hall recordings.
The M50s are very pleasant but in that midrange area are slightly softer (duller) than the M22s. If you listen to cymbals on an M22 and switch to the M50, the cymbals are a bit less clear. But these subtle differences are really only easily noticeable on instantaneous A/B comparisons with a switcher.
The virtues of using a satellite "bookshelf" size speaker with a subwoofer include easier placement. You can actually put them on a shelf, close to the wall behind. You can even wall-mount them if you wish. With floorstanding speakers, sometimes putting them too close to a wall or corner will result in exaggerated or boomy bass. Since bookshelf size speakers don't have much bass response, that isn't a problem. The subwoofer reproduces the deep bass.
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