If a disc has a stereo track, you would want to select that. For discs that don't I choose DD and have no lack of sound. You may not get exactly what was on the LFE channel in the downmix, but there will be sufficient bass. I don't have a sub in my second system right now, but I tested it in my regular rig and it works fine. It obviously isn't the same as it would be if it were discrete channel information.