I googled your 5.1 headphones and they use USB for electrical power and standard 3.5mm minijacks to get the audio signal from the soundcard.
Either the headphones are faulty or your soundcard is not setup correctly/faulty.
You will need to test to isolate the cause of the problem.
At the moment you say that when using the realtek 5.1 sound test, you have stereo audio coming from the front left and right speakers (green 3.5mm jack output), try putting the other coloured 3.5mm jacks into this green soundcard output and see if the test sounds still play to determine if the other speakers inside the headset are working. Bear in mind that one of the 3.5mm jacks on the headphones are for the mic and wont play any sound and you may not hear the bass signal very well.
After you test like this youll know if the headphones are working correctly or not. If they are working fine then the soundcard is not setup correctly (or very unlikely it could be faulty on the surround outputs). If the headphones are fine and you are still getting no audio signal from all the speakers when running the 5.1 test you should download different realtek soundcard drivers available from your motherboard manufacturers website. Its always a good idea to get the latest drivers and not the ones that come supplied on the motherboard drivers disk.
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Also make sure that the headphones connectors are all plugged into the back of the computer as the front panel audio output is for stereo only.
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