That post in the AMD forums is wrong.
What format audio are you trying to use? The HD2600 only supports 2-channel LPCM and multi-channel AC3 5.1. It does not support LPCM 5.1.
Are you using the AMD DVI2HDMI adapter? You need to use theirs or a compatible DVI2HDMI that carries audio, most do not. Monoprice sells one. If you are using AMD’s, only one of the dual DVI slots will carry audio. Take a look on the back of the card to see which you are using and try the other.
