see if there are any new drivers for the soundmax. Regardless, I would uninstall the soundmax driver and reinstall them. Also check to see if there any hardware conflicts that is affecting your soundmax.
The driver install switches the default sound device to the output on the card.
Go to sound properties and set playback device to your onboard sound .
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I had the exact same problem! Same dc7800 and same Asus EAH4350.
Seems during the install of the ATI drivers the onboard audio is disabled in the BIOS
Re-enable it and reinstall the drivers (if you need to) and you should be good to go