Actually a video card has got nothing to do with sound of any kind. The card is just responsible for handling graphical duties, not process sound. Try updating your sound drivers.
ATI sound through HDMI... video and sound is a reality on ati cards.
OP.. did you open up the sound in control panel and select the device you wanted ? Also, did you try uninstalling all ati drivers and the doing an advanced install when you reinstall so you can deny the installation of the sound drivers and only install the video driver ?