There are some good points above, but here's a contrary view for what it's worth--I've also used the Phantom mode on my pre/pro to avoid using a center speaker. This works alright if you are sitting in the sweet spot and the two main speakers are able to "image" the center channel info in the middle where it belongs. But the people who are sitting off-center won't have that imaging and the center channel info won't be anchored on the screen the way it would be with a dedicated center speaker.
I've experimented with both same-make and different-make center channel speakers. My current center is of a different make. I think the whole timber matching case for the three front speakers is a bit overstated when it comes to movie soundtracks. Yes, you can hear a slight difference, but even my same-make speaker sounded different, although to a lesser degree. Does that translate into much when watching movies? In my experience, no. I find I am much less tuned into those sorts of things when watching a movie, and very rarely notice the slight timber mismatch.
My system does double duty for audio and HT. The way I have it setup doesn't compromise the audio portion at all. By doing this, I'm able to afford higher quality gear than I would have if I had to go with two separate systems. It's all a matter of money and space. The center is by far the most important speaker in an HT system. Put the money you would have spent on five new HT speakers into your center channel. You'll thank me later. Good luck.
