Magnificent work zeromus, thank you so much! 
The github code works after a slight rewrite of the decrypt loop ending condition (e.g. cast the file header buffer directly to char* instead of going via int).
That discovery you made about the unpacked music in the dos-version should suffice to circumvent the need of using it for the only strictly legal purpose though, so that’s good to know! Personally, however, I wanted to use the unpacker for something a bit more shady (getting the Drek animation the lazy way), but I can’t imagine the devs would have any problems with it given that it’s being used for private purposes only… O.o