There is a common misconception that Dolby Digital Plus is only a Multi-channel solution. Dolby Digital Plus as an audio codec can deliver a stereo experience as well.

Dolby Digital Plus provides distinctive audio benefits both as a 2-channel stereo or multi-channel surround sound vehicle. Playback on laptop speakers benefits form (among other things) advanced Dynamic RangeControl (DRC) that uses the metadata included in the Dolby Audio stream to play back the audio optimally even on small speakers. 

Additionally when your PC is connected via HDMI to a multi-channel home theater system,the full surround sound detail is supported. Finally, for laptops that include Dolby Post Processing (a solution that OEMs can choose to include), Dolby enables headphone virtualization to simulate a surround sound experience over headphones when listening to a multi-channel audio track.