Ok, reading through the thread again it seems like you've checked the obvious culprits. But, just for the sake of a sanity check lets look at some troubleshooting steps. First, linux will in some cases select the the wrong sound output hardware depending on integrated sound or an add on card but that doesn't seem to be the issue here. Second, I would check the fusion.ini and make sure the sound is not disabled. Third, and just for the sake of trying it :
Set Sound Preferences
If you use a PC with an integrated audio device and it has no sound when playing a media file on a player, try these simple steps to set Sound Preferences for your PC. It works for me for the audio device I have.
Go to Menu > Applications > Preferences > Sound to bring up the Sound Preferences window.
Under the Hardware tab, change Profile to Analog Stereo Duplex from the drop-down menu.
Click "Test Speakers" to check if it works.
As the items available from the drop-down menus might differ depending on the hardware devices detected by the system, you might want to try other items in the menus to see if they work for your devices.