Newbie 5.1 Problems, with Logitech 640 and Turtle Beach Santa Cruz

[stilz]

Hello,
I've finally got my hands on a 5.1 setup, as titled suggested, the Turtle Beach Santa Cruz sound card and Logitech 640 5.1 speakers. I installed and setup everything, change the setting to the 5.1 in the sound card menu, and played a MP3...but the sound only came out from the two front channels. I get 4 channels when I play a video file say Naruto. Is that because those files only have data for so many channels?
Then I tested an APE file, still only two channels of sound. The weird thing though, is that I'm sure there are sounds that are missing, which I guess are suppose to come out from the other channels but don't.
Previously, I used two sets of independent speakers and tried the 4 channel setting with them, and the sounds come out from all 4. Is there anyway to set things up so the sounds come out from all channels despite its not being Dolby or 5.1 or whatever?
Apology for the wordiness, thank you for your help.

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