I just got an Onkyo HT-S770 and am having a little bit of trouble selecting different surround modes. My dvd player is connected with an optical cable to my reciever. The problem is I can only switch between Dolby Pro Logic IIx Cinema/Music/Game and Dts Neo 6 Cinema/Music. I cant seem to switch to Dolby Digital which is what most of my dvds use. These are the only options I can switch between when selecting the listening mode. Any help would be appreciated.