Here is a close-up view of the Digital Audio Coaxial Inputs.
These connections are used to access Dolby Digital or DTS surround sound from DVD players, Digital Cable Boxes, Satellite Boxes, or other source component that has either a Digital Optical or Digital Coaxial output connection. Some devices have both options, in which case, you can can choose either.
It is also important to note that some CD-Only players have digital audio outputs as well, however, these are just two channel outputs.
In addition, just above the Coaxial Digital Audio inputs is the XM Satellite Radio input. The XM Radio input allows the connection of an XM Tuner/Antenna (paid subscription required for program access).