This may not help much, but I have the same issue with the DX58S0 and Win 7, so maybe it's something to do with Win 7? I installed new drivers for it dated 8/5/2009 and the same problem remains. Like you said, it plays the *tests* fine, through all speakers using the sound applet in control panel and the Realtec control center, but when using any audio player it only plays through the fronts and sub. Games that support 5.1 still only use 2.1 as well. I'm still searching for a solution!
Same thing here, tests fine, but most times not even stereo, much less 5.1
Please someone shed some light on either what to do or when to expect some new drivers.
I am also facing the similar issue. On windows7 OS i am unable to play 5.1..... Subwoofer and center speaker doenst not give any sound, however windows 7 inbuit sound configuration utility plays sound in all 5 speaks when tested. Doesnt anyone know any solution for this???????????