S/PDIF Out vs. Realtek Digital Output

Okay, so here is my problem: I have a Dell XPS 730x with an X-fi Titanium soundcard that has 2 optical outputs in addition to the traditional analog outputs.  One optical in and one optical out.  I recently purchased the Logitech Z-5500 speaker system to replace my old Dell speakers, in hopes of utilizing the optical connection.

Now here's the thing.  In my playback devices, I see both an SPDIF out option, which seems to work, albeit with a slight delay at the beginning of any sound, AND a Realtek Digital Output, which does not work, no matter what I try.

So I guess my question is, are these two the same thing?  They both have the same icon, and are both digital outputs, so it baffles me why one would work and other not.  And yes, I have already installed the latest Realtek drivers, to no avail.  Though their HDMI driver works fine on my system when I hook up my TV.

I'll be happy to provide any additional details upon request.  Thanks for reading!