These two options assume that you have a Dolby Digital signal, and it depends on whether the Dolby Digital signal is 2.0 or 5.1. In a 5.1 system and with a 5.1 source, then DD+PLII-C isn't going to be an option (you already have all six channels in the original source, so adding mode via Pro Logic II processing is impossible). For Dolby 2.0 sources, I use DD+PLII.