I'd suspect that your signal strength isn't optimum. The only time I get breakdown of audio or video is when it's stormy or thickly overcast and my DSS receiver's antenna strength goes from a typical 76-80 to 50 or lower. Obviously Dolby 5.1 audio is much more to send than standard audio. Your antenna aiming or geographic location may just not get you enough of the signal to make it all sound clear. If your Dolby receiver sounds OK with 5.1 DVDs then it's probably your DSS setup. You might also double check the digital cables from your DSS to your amp. A bad cable might be the easiest thing to replace. The optical or RCA digital cable is only used if there's a dolby 5.1 signal, so they may easily be the culprets.