Ideally, all the speakers (other than the subwoofer) will be identical. However, the front to back matching is far less important than matching across the front. When a sound pans across the front, you don't want it to change tonal quality, and that means you want the front three speakers to be "voice matched", which, again, ideally would mean having exactly the same speaker in each place. But you can use the same manufacturer's matching center speaker if you prefer.
The reason why front to back matching is less important is because of the way the channels are typically used, as well as the fact that you can't hear as well behind you as in front of you (which is one reason why people tend to face things they want to hear; the other reason being that they often want to see them as well).
