The higher-end Logitech systems have always sounded excellent to me, far better than Creative. They actually use some rather nice drivers (relatively speaking) from TangBand Speakers, a name i got to know from DIY speakerbuilding before i found their products in the Logitechs. Give them a listen....
Edit: I notice, though, that Logitech doesnt really have a good 5.1 offering... its the 4.1 i'm thinking of.