Sony PCG-XG28 Primary User Manual page 84

Insert the DVD-ROM drive into the multipurpose bay and connect the
OPTICAL OUT connector to a Dolby Digital Decoder integrated device to
experience Dolby Digital recorded videos and dynamic sound.
Switch the Digital output to PCM when you connect a device that does
not support Dolby Digital, otherwise, the speakers or your hearing may
be damaged by the increased volume. Switch the Digital output to PCM
when you play DVDs that support linear PCM recording on the Mini
Docking Station.