Creative Sound Blaster X-Fi User Manual page 10

11.
SPDIF I/O connector
Connect the Optical Digital IO Card* to this connector.
Notes
*Available with some models of your audio device, or as an upgrade
accessory in some regions.
Select the Digital I/O option when connecting digital audio devices to the
Digital I/O Module (available with selected models or as an upgrade option).
Also select the option if you want to connect external digital audio devices that
accept stereo PCM or compressed Dolby Digital/DTS Bitstream from the
S/PDIF output. See Configuring your FlexiJack for more information.
Some models of your audio device come with a built-in 64 MB X-RAM. This
special RAM is reserved for game developers to store a game's audio file on the
audio card, for faster retrieval, processing and playback. Any game that supports
X-RAM receives an even bigger performance boost.