If the HPM-900s have a somewhat elevated mid-range(I'm not familiar with them), the M22s aren't going to duplicate that effect. Both the M2s and M22s have an exceptionally accurate and flat mid-range which I consider to be ideal for music. The M22s, with two rather than one driver in that range would be able to play louder with low distortion, but this wouldn't affect moderate listening levels.

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Enjoy the music, not the equipment.