I used to run the Cobalt 806s and center channel in my system a LONG time ago. The Cobalts used a inverted dome titanium dome tweeter. The Chorus uses a inverted dome aluminum/magnesium. I have heard the Chorus a while ago. I would agree that it is probably your best bet in matching the side channels if you want something right now. You could try to look for an Electra CC900. This also uses the Cobalt titanium tweeter as well.
You could keep looking on ebay. There was a Cobalt CC800 center that just sold on May 11 for $149 (just missed it!). Or you could grab a pair of 806s bookshelves and use one for center.