Yes, I know that's what you're trying to figure out, but the solution might not be acceptable: connect the sub with speaker wire to the speaker level inputs instead of running a coaxial cable from the receiver's sub output. Of course the bass management of the receiver wouldn't be available and you'd have to try to blend the sub output with its low pass filter control with the "natural" roll-off of the M22s.

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Enjoy the music, not the equipment.