For Digital Speakers
SPDIF Out
Plug the optical TOSLINK adaptor into the S/PDIF-Out combo connector. Then, connect your decoder’s S/PDIF in port to the optical adaptor with the TOSLINK optical cable
You can also use a coaxial cable for a S/PDIF connection. Just plug the coaxial RCA male connector to the S/PDIF-Out combo jack and connect the other end into the coaxial S/PDIF input on your decoder.
SPDIF In
Plug the optical TOSLINK adaptor into the S/PDIF-In combo connector. Then, connect your MD/CD/DVD player’s S/PDIF out port to the optical adaptor with the TOSLINK optical cable
You can also use a coaxial cable for a S/PDIF digital connection. Just plug the coaxial RCA male connector to the S/PDIF-In combo jack and connect the other end into the coaxial S/PDIF output on the player.
ASUS Xonar D2X Quick Installation Guide