Michael, I'll adopt most of what sushi said. The ideal for a center speaker is one that sounds as nearly as possible the same as the mains. So, besides using a third speaker exactly the same(which is sometimes feasible, especially in a setup with a front projector), a smaller speaker having the same midrange and treble response is a good alternative. Obviously this speaker should be positioned vertically(God didn't intend that we listen to speakers flopped over on their side)where it has better horizontal dispersion than the typical MTM arrangement(the unique VP150 configuration appears to be a significant improvement). This is what appears logical and sounds better to me than any MTM I've ever heard. The height of the tweeter and distance above the screen has been no problem in my experience; with a small speaker the added height compared to a horizontal speaker might be a matter of 3-4", and would be zero if the speaker was turned upside-down. In any case, whatever the speaker, it should be tilted down if it's too high so that the tweeter points at ear level.
