I am also Newbie and have the same problem!
Though I can get sound from RCA both from Centrafuse and Windows.
I thought it could be the amplifier that was disfunctional and had a friend to look at it inside, but there was nothing to see and the IC chip on the amplifier looked fine. He haven't tried to measure the power through the components, but that is the next step.
I will try to reinstall XP and all the drivers again, before taking the next step.
Do somebody have another suggestion?