How do you have your speakers connected?
Most sound cards do not provide 5.1 output unless specifically designed to do so (not sure about yours, but a multi-input/output is not likely to).
Generally the connections on a multi-channel card are only L and R, with the odd numbers being L channels and the even numbers being the R channels.
Sounds like maybe you only have your speakers hooked up to the #1 output in your sound card, which would be a Left only connection.