This is built to further extend Dolby Digital Surround EX (DD-EX). This could be considered a 7.1 channel system. As opposed to DD-EX, which has an added channel in the center rear, THX-EX puts 2 more channels in the rear, so there is a front left, front right, front center, listening position left, listening position right, rear left, rear right. It uses Dolby Digital 5.1 as a base and matrixes in the extra 2 channels into the rear channels similar in fashion to Dolby Pro-Logic and Matrixed Surround. It is going to be available exclusively in THX Ultra certified products.