The RSX-1055 and RSX-1065 surround receivers have 3 different 6.1/7.1 surround formats available for digital sources – Dolby Digital EX, dts ES, and Rotel XS Expanded surround.  For all dts soundtracks dts ES will decode additional surround information for the center back speakers. With Dolby Digital soundtracks however the default setting for the unit is to use Rotel XS Expanded surround for your center back information. To switch the default mode from Rotel XS to Dolby Digital EX, press the ‘+’ button on your remote control to cycle between both surround modes. Changing the mode to DD EX will set this as the default 6.1/7.1surround mode for all future Dolby Digital sources.