Can somebody please clarify on formats. DTS and Dolby digital are basic choices for digital surround sound. I thouight THX was just an enhancement to the cinematic sound quality on an individual movie but I now see you can purchase THX speaker systems etc. Please help to complete my knowledge and explain THX. Does this actally rival DD and DTS contrary to what I thought, or is it yet another option we have to upgrade our equipment for in order to benefit.