When Damian left he should have summoned a couple Black Ring soldiers for you to fight. If they never showed up that may be why the teleporter didn't work (it is disabled, waiting for the end of the fight that never happened).

Try emailing support@larian.com, with a description of the problem (see DKS support). I believe the second DKS patch prevents a possible bug with missing opponents, but if the problem already existed the patch can not help. With your save Larian support can fix it, though.

Re-installing the game should not impact your saves, though you may want to back them up, anyway, just in case. Before re-installing there is a configuration file in pretty much the same place as the saves, which you could try deleting (or renaming) and see if forcing the game to re-create it gets the sound working. There is one file called graphicsoptions.xml, but I don't know if that is exclusively graphics settings...

In XP the saves are in the folder

C:\Documents and Settings\ %username% \Local Settings\Application Data\Divinity 2\Savegames

or in Vista / Win 7

C:\Users\ %username% \AppData\Local\Divinity 2\Savegames

You may need to set Windows Explorer to show hidden files and folders (XP, Vista, Win 7).