Asus P6T - Motherboard - ATX User Manual page 61

11. Optical drive audio connector (4-pin CD)
This connector allows you to receive stereo audio input from sound sources
such as a CD-ROM, TV tuner, or MPEG card.
12. Digital audio connector (4-1 pin SPDIF_OUT)
This connector is for an additional Sony/Philips Digital Interface (S/PDIF)
port(s). If you are using ASUS HDMI-equipped graphics card, connect the
HDMI card to this connector with a S/PDIF out cable.
The S/PDIF out cable are purchased separately.
ASUS P6T 2-37