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!
After looking even more at comb filtering effect posts and research on the 'net, the T-shape, dual center speakers (with the horizontal VP-180 just ABOVE the TV/Screen, angled slightly down toward the top of the ear level at the seated position and the vertical M80 below the TV/screen, angled ever-so-slightly up toward the ear level at the seated viewing position), seems to be widely raved about. In many of the high-end audio forums, especially with users who have large home theater spaces, they speak very highly of adequately powered dual centers in that arrangement (which ties in to everyone's views on this board that the best possible arrangement is three vertical speakers across the front), pointing to great dispersion across the whole room as one of the main benefits.
I think that's the new long term plan, especially since it poses far less difficult mounting challenges. (Angling the VP-180 downward just requires an angled shelf with a lip on the front to hold the speaker in place-immensely less of a hassle than trying to angle an M80 downward near the ceiling).
