Actually truth be known, 6.1 and 7.1 are really one in the same. while DTS calls the DTS-ES 6.1 THX refers to its THX-EX Ultra as 7.1 both include the rear channel. While some claim to provide 7.1 channels it is not a true standard and the rear channels are mono even in a 2 speaker configuration. If you go to google and search on DTS-ES and on THX-EX you will get some very good explanations of both standards.