The EP350 should not sound boomy if it is correctly crossed-over, level calibrated, and well-placed. In case you have already covered the former two items, the culprit might be the sub placement as others have suggested.
Have you tried the technique of "subwoofer crawl" to determine the optimal locations of the sub in your room yet? Basically, you temporarily place the sub on your normal listening position, play some bass-heavy music, and crawl around the room to identify a spot(s) where the bass is heard powerful yet balanced, tight and non-boomy.
With regard to the M22s sounding thin, I again agree with others, and it may well be due to the placement. What's the current distance between the M22s, as well as the listening distance?
