So my sound card supports 7.1, and all speakers output the correct sounds in both the driver software and windows sound configuration screen, but I pop in 5.1 content in VLC and WMC and everything still outputs as Stereo. I'm fairly sure that Sharknado supports Dolby Digital 5.1 as it says it on the back side of the CD case. I'm running Windows 8.1 Pro, but I'm not sure what other things could be causing this.

Your video player set to 5.1 playback?

Does your soundcard menu have a speaker test? Does that work correctly?

Yes, all media players are set to 5.1 playback. Both the sound card sound check and the Windows sound check output the sounds in their correct locations.

Depending on the player, you may need to check settings for individual decoders as well.