You can extract all game related files using the GFXFileManager. You just need to write a tool that uses their GFXFileManager.
I've made an example for listing files in a container using my public library:
You can use this to access the files using their GFXFileManager.dll. You just need to figure out the password ... which is quite an easy task with this lib aswell.
Alternative: Take one of the released extractor tools and patch the decryption part to match theirs.
as @
said ... it's not that easy ...