I would suggest staying with a single center. Having two can create more problems (cancellation, etc.) than one. The would also need to be the same ohms and have similar crossovers, etc. I would spend the dough and buy a beefy center channel. I use the Klipsch THX LCR for the center. Before going to this monster of a speaker, I always thought the center channel was drown out. The center should be the best speaker in your system in my opinion (for movies anyhow). After all, like 80% of a soundtrack comes from the center.