Brief explanation of MTM.
The centers you've seen(linked today) are all MTM. It means...mid-tweeter-mid. It causes "issues" with sound off-axis. The "completely proper" way to do 3 speakers is to(like a somewhat seriously suggested above with the Ebay linked speaker) have all three be the exact same speaker.
To do that requires you to have the space to actually do it. There is only one room in my home that has a "non-traditional"(read MTM) center. It is my office outfitted with 4 Infinity Crescendo 3007 and the remnants of a broken 3006 that I built my own center/TV stand with. I basically made a big box, internally mimicked the cabinet the 3006 originally had...mounted the drivers/crossover. Sat the TV on it.
Cause I have mad woodworking skills. And I have an enormous SACD/DVD-A collection.