Regarding center channels - I am not an expert, but like you I did a bunch of research which led me to switching out my VP150 for the M2. I believe that 2 center channel speakers are very doable (CatBrat has done it among others), but must be done in the correct configuration to avoid weird effects or interactions with each other. For example, 2 vertical center channels would not make sense placed beside each other as you are simply starting to create another horizontal array but in a non-controlled way and you start getting into all of those horizontal array issues again. However if the speakers are separated you should start to get away from those issues. So to my logic, the only way to have 2 center channels with ample separation is one above and one below the screen. From there you get into 2 verticals, 2 horizontals or a vertical and horizontal mix as your options. I personally have never heard dual centers, but having above and below screen seem to have worked for a few forum members at least.
Starting with a good horizontal (or vertical) center speaker and then trying options from there makes a lot of sense to me!
