I would argue that, more than anything else, the THX certification means that the manufacturer was willing to pay George an outrageous sum of money. Of course, George probably isn't going to give one to something that sounds like crap, but I don't have any particular faith that it's going to sound better than another component that isn't THX labelled.

In the end, anyway, is the fact that even the THX people tell you that just because it's THX certified doesn't mean that it's going to sound great in your room. Only in their highly optimized listening environment. The obvious answer would be to get what sounds good in your room, but, then, travelling audio salesmen are hard to come by these days.