Send me a file sample.
Edit: Just see this is a unreal engine game with just 2 big paks, plus the files seem to be encrypted with a aes key, therefore it could be the case you have to use xtool ue4 plugin with the key below and then use precompression (I don't know if it is zlib or oodle or something else).
The key is
Code:
0xE01312D26CAD1529142D3ACA6DB25D4091C1AAFE0C91E5DC104C36A768DB1E50