One note though, some THX certified gear IS actually better than other non-THX certified gear. By that, I mean, I have a THX certified receiver, but only because the receiver had all of the features I wanted. The particular brand didn't have what I wanted in their non-THX line.
So, a THX device may really sound better, but not because of the THX stamp on it. Only because many times the manufacturer puts better components in it than in the rest of their product line.
Personally, I'd skip it, or at least don't pay for it.
