If the digital 5.1 is for movies or music, you might also consider Videologic's Digitheater 5.1
It'll run you $185+ shipping with the decoder or $95+ shipping without. Either way, it's a good system now that the price has dropped.
This speaker set will not compete with the aforementioned Klipsch and Logitech ~$300 systems in terms of loudness, so if your room needs to shake, don't expect the Digitheater to do it quite like those.
You can check out the review
here
note: it didn't perform as well in a 4.1 gaming mode, if that's a concern for you