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
Just wondering if this unpacker tool is still somewhere out there?
The included packer program in Verge 3 (which appears to be the go-to version) doesn't work with the files in Diver Down..