For your setup I was suggesting using a single M2 as a center speaker. On the speaker ordering pages there is an option to add only a single speaker to your cart rather than a pair.

3M80 2M22 6QS8 2M2 1EP500 Sony BDP-S590 Panny-7000 Onkyo-3007 Carada-134 Xbox Buttkicker AS-EQ1