Aha - looks like it's still OpenAL messing with you, then. Could you run a search in your C:\Windows folder for any OpenAL*.dll files and delete them? There should be a system32/OpenAL32.dll and possibly some others. That... should be safe, provided it's done carefully, And it also shouldn't break other applications on your system. But as always, messing with files in the windows folder should be approached with caution.
Basically, I think the issue is that there's a corrupted version of the OpenAL dll in the windows folder somewhere and that's being used instead of the one that the game comes with, despite being explicitly told not to. Usually, installing OpenAL (like you did) fixes the issue, but it doesn't seem like it did here.