How to add center channel to stereo

I 2nd the ZVOX. I just added one to my television in my living room due to the poor sound quality. I'm really happy with the results.

Accuvoice processing on thé Zvox soundbar makes a very noticeable difference to the resolution of dialog.

thanks. I guess I'll be proceeding along those lines.

REUBENT nailed it succinctly ..... full stop.

If you want to introduce a stand-alone CC discrete speaker, then it  is on a discrete encoded channel requiring a multi-channel AV preamp/ processor to decode. 

I'm not aware of any way to steer dialog to a center speaker without a processor. If you start down that path, you're going to be adding either a HT receiver or a processor and amp, as well as the speaker itself.

If you just want better dialog, you might try something like one of the ZVOX Soundbase or Soundbar models. They make 9 or 10 different models at different price ranges. They seem to be effective and very well built. Go to the ZVOX website for information on all their models.