Unless you are really going to lose all interest in watching movies because of a little reflection off your Speakers, I wouldn't worry too much.
Of course, I say that as a person that likes some amount of ambient light in my room when watching anything... Oh, and I don't spend nearly as much time in HT as I do Music enjoyment...
But other than that...
Are you the kind of person that keeps your Grilles on? That will reduce reflective surface area on the front. For the sides, you could make a "sock" with Speaker Grille Cloth that you could just pull over the Speaker if necessary (and that way avoid doing anything to the speakers themselves).