Just an FYI, MTm have a different lobing pattern than your tyopical 2-way or 3-way. Setting an MTM on it's side is not a good center channel. You are much better off using your L/R's as centers or using a W-T/M-W as a center channel. Due the lobing effect created by an MTM you do not get much vertical dispersion. In fact this was Dr. D'Appolito's desired effect when he came up with the original MTM. MTM's provide a more focused sound and therefore better imaging. When laid sideways you get almost zero horizontal dispersion.

Here is a reference to what I am talking about.
http://nousaine.com/cen%20chan%201.htm
http://www.birotechnology.com/articles/VSTWLA.html


If you listen to an MTM on axis seated you get very good imaging and a balanced sound if designed well. If you stand up the midrange gets sucked out. Now turn this on it's side, and you can see what happens. Go to the bottom of this page see the graph and you will understand what I am talking about.

http://murphyblaster.com/content.php?f=gem_mod.html