Try using a known 5.1 sound source, like a good movie.
The music is likely only 2.1, so the other speakers may not be used.
If your realtek manager is the same as the gigabyte one (I.e. gigabyte didn't modify the layout), there should be a play button on the screen for your output settings (The thing with lots of brightly coloured circles), click it and it should play each speaker sequentially. If it works there then the problem is simply the file your playing, it is 2.1... if it doesn't then try mucking around with the plugs going in (move them around a bit).