Oak, my thought is that you'll be happy staying with the M2 for both front and back center. But before you even think about the VP150, experiment; get completely set up and listen with the M2 front center. Then use the "Quad-Field" feature of your 2300 to create a "phantom" rear center speaker and see how that sounds. Then switch the M2 to the rear surround(with the M22s handling the center channel in phantom mode)to see how that sounds. The M2 should be a near-perfect match with the M22s.

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Enjoy the music, not the equipment.