Short answer is that most of the time 2 center channel speakers isn't as effective as you might think.
Don't get me wrong, I've done it myself back with my 1st theater space many years ago, but I did so much experimenting with audio, it was far from normal. I had 2 center, front left, front right, 2 more speakers between the center and the right and left in the front, side surrounds, rear surround, multiple subs. This was all when DVD was just coming out, Dolby 5.1 was new, and DTS 5.1 for the home was barely ever heard of.
I did all sorts of power combinations, and signal combinations/splitting to get an immersive sound, and people that came over really liked it. Then again, nobody else that I knew had a home theater either.
I would trade all of that for a good solid 7.1 setup with a single center speaker, no goofy other add-ons or circuit boards combining and splitting channel signals. Oh wait, I did.
Keep in mind that you need to be able to drive 2 center channels as well. Just plugging them both in to the center channel "jacks" on your receiver may not work.
One last thought. If you get the center channel at listening height (seated ear level) of the first row, you should have (typically) no more than 12 inches of height from that to what would be the 2nd row listening height. From just about any reasonable seating distance, the audio will easily cover both areas very well.
I have a VP180 behind my AT screen. It is on a stand that I made to put the tweeters at ear height of the first row. The 2nd row is 12" taller, and there are no issues at all with the center channel sound quality.