Before going to a subwoofer, make sure you have tried the Maggies with a powerful amp (at least 350 watts into 4 ohms). It really does make a difference. (My amps are 600 wpc). You didn't mention which Maggies you have. My MG1.6 are really good to 40 Hz or so, and there is not a lot of music that needs lower.
That said, I do have an elaborate subwoofer system, but depending on your musical tastes it might be overkill for you. Try the big amp first.
That said, I do have an elaborate subwoofer system, but depending on your musical tastes it might be overkill for you. Try the big amp first.