If DVD player has 6 channel discrete output, it is doing the DD decoding and if you connect this 6 ch output to your speaker's 6 ch input you will get DD sound. TS STB does not have DD decoder. It only outputs DD signal thru HDMI and optical ports which needs to be decoded externally by an amp. If your speakers don't have HDMI or optical inputs for the built in amp, it cannot decode the DD signal from the STB directly. Therefore you can only use the L/R ports to get Dolby Prologic or use an external amp which can first decode the STB's DD signal to discrete 6 ch output for your speaker.