I honestly think you are better off leaving the Maggies as an audio only system rather than trying to have them do double duty. If you absolutely have to use them in a combined HT and audio setting, I would recommend that you skip the center channel, buy another identical pair of maggies as surrounds and use your Receiver in Phantom Center Channel Mode.
My recommedation, though, is to keep the maggies for music and get a dedicated 5 speaker HT system from the same mfg that is allready properly matched. I think you will find it very difficult to match up a center channel to the maggies.
Just my .02
