I'm quite sure to have already seen this format in the past since I remember the index file located in a sub-folder of the dat archives.
Anyway I made a new script from scratch:http://aluigi.org/bms/dirt5.bms
Just select dat.ndx and it will do the rest.
Most of the files are without name and it's normal because they are not referenced so I decided to extract them anyway (maybe there is some old/hidden content)
Thanks a lot for the script! Sorry for the late respond, only now I saw your post. It worked, but there are a couple of problems =(1.
In process of unpacking files at some point the following error appears: https://imgur.com/Mrtmobx
But there is no 9_DISC_XB.dat file in the dat folder. That's all we have:
It seems all the *.cfg or *.json or other text files are not readable (encrypted or compressed?). I've attach the zip archive with some of this files.
Is any chance to extract all files from .dat and make them readable? (*.cfg, *.json etc)
And thanks again for your hard work! Many times your scripts helped me to modify games =)