I know this is an old thread, but just wanted to chime in that I bought a used pair of CS6 a couple weeks back. The seller had bought them at an auction, as they came from a dealer that had gone bankrupt. I paid a quite reasonable price, got them home (after almost 800 miles of driving to get them and bring them home), hooked them up and they sounded horrible. Came to the conclusion the tweeters were fried after talking with Tim in Thiel service, who was fantastic.
More to come, but $162 later I got new tweeters delivered today via UPS, installed them which takes all of about 30 seconds each, and played them for about an hour on a variety of music. Night and day, the tweeters were what these CS6s needed, and with absolutely no tweaking of setup, toe-in, etc. they sound fantastic. I also have a pair of CS2.4s (which led me to seek out the 6s), and while those are great, too, the CS6 is a true full range speaker.
Now I need a center channel that pairs well...any suggestions? Thanks!