No digital signal detected during rosetube play back

How can i detect digital signal during Rosetube play back? Only PCM signal was found even i chose some DTS video clips to play. Please help!

RS201 does not have a built-in DTS/DOLBY codec.
RS201 only supports 2-channel stereo sound sources.

If you have a receiver that can play DTS/Dolby, you can listen to the sound using the HDMI Passthrough function. If you select HDMI output in the input/output setup menu and turn on the HDMI Passthrough option, audio data is bypassed and transmitted through HDMI when playing content.