Un, if you examine the M22 and M40 measurements taken at the NRC as part of the SoundStage reviews you'll note that the M22 actually measured slightly lower in distortion at the same high 90dB level. This would indicate that it should handle your size room at least as well. Since you'll be using a sub, the better bass extension of the M40 shouldn't be a factor. The somewhat smoother M22 mid-range would be a bit more enjoyable, I would think.

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Enjoy the music, not the equipment.