Pretty much. The soundcard is simply taking an uncompressed 5.1 stream and converting it to Dolby Digital via Dolby Digital Live, then sending that signal via optical to the speakers, which then converts the digital signal to analog.
If you want to run a test, you can play back an already existing Dolby Digital file, to make sure your speakers can play it back fine (if they're a 5.1 set using optical, I'm sure they can. A test never hurts though).