I can't find any info on what type of speaker to get when I go to 6.1 from 5.1. Should I get another Dipole/Bipole speaker like my surrounds...or should I get a center channel speaker (the typical W-T-W) because it's a rear CENTER channel? I have Phase Tech PC 3.1's for the fronts and center and Phase Tech Dipole/Bipole (switchable) surrounds if this helps. Any suggestions or comments would be helpful!