Need sound card

Technically, if your main purpose is Dolby/DTS when watching movies off a DVD/Blu-Ray, then any soundcard with optical output will do.

If you want Dolby/DTS when doing other things that do not already have a Dolby/DTS track [games, for example], then you need a soundcard with either Dolby Digital Live or DTS-Connect support.

The Turtle Beach card will suffice for either purpose, though I note there are plenty of alternatives from ASUS and HT Omega at the sub $100 price point.
If the movie already has a Dolby/DTS track, any optical output can carry the signal without issue. Even the motherboard optical output can pass through already existing Dolby/DTS audio tracks.

The reason soundcard encoding is needed, because games and other non-movie sources typically do not have a Dolby/DTS audio track. So the soundcard needs to encode to one of those formats in realtime in order to get 5.1 via optical.