Asus Xonar D2X Guide D'installation Rapide page 9

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
9