L7, I suppose that I might as well join Craig and 2x6 in being puzzled by the "huge" difference in bass reported. Both measurements and listener reports indicate that the M60s have excellent bass and a kickdrum isn't really all that severe a test. One seemingly unlikely point that I've mentioned before, because it's actually happened twice here, is to make sure that the M60 woofers are actually operating by making sure that the connecting straps on the speaker terminals are tight(the 750s have none, of course).

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Enjoy the music, not the equipment.