Better than almost anything you can buy in this price range.
This is going to be hooked up to a Panasonic 50" 1080p Plasma HDTV. These are the ones I'm looking at:
Klipsch Quintet SL System
Klipsch Quintet III System
Reviews of the Quintet III are great, however, I get a very good deal on the SL (as well as the Quintet III), so does anyone have any knowledge or experience with these?
I would listen to the Definitive Tech ProCinema 600 ($799 MSRP) and see what you think. Personally I think DT's sound warm and full, but other people think they sound flat and muddy. Same way some people love Klipsch, and I think they sound bright and harsh.
Best bet is to find a real home theater store and test out what they have. Most real HT stores will let you do an in-home test of their speakers. It's really more about what sounds best to you personally; it's a very subjective purchase.