The way DTS 2.0+ Digital Out works is that it can recognize incoming DTS audio streams (such as a 5.1 channel stream), decode it, and then downmix it to 2-channels for playback on the TVs built-in speaker system.
However, in addition, it can also pass an undecoded incoming DTS bitstream through the TV and back out to a compatible home theater receiver or sound bar via the TV's digital optical audio output connection, or via HDMI using Audio Return Channel. The receiver or sound bar can then decode the DTS bitstream for up to 5-channel playback (or more) according to its capabilities.
The incorporation of this new feature gives compatible TVs the ability to handle both incoming Dolby Digital and DTS bitstreams that may be available from Broadcast, Cable, Satellite, Internet, or other connected sources.
For more details, read the Official DTS Announcement