Why is there no sound when I use S/PDIF-in signal?

If your speakers are connected via S/PDIF-out, please go to AC'97 Audio Configuration (Sound effect icon at your system tray) and set the S/PDIF-out to "S/PDIF-In to S/PDIF-Out pass through mode".

If your speakers are connected via Speaker out/Line out, please go to AC'97 Audio Configuration and in S/PDIF-In, check the box "real time S/PDIF-In monitor".