How To Extracting Files From Rom Already Cooked

[PATRICKJ]

hi!!
i downloaded llbasha-WM5-AKU35pp16c3 rom
i want extract os.nb file from nk.nbf with typho5 utility (typhoonbftool_v5),i got this error:
unknow header format, and it abort work.
other way:
i want extract os.nb file from nk.nba with prepare_imgfs, and i got this error:
searching for IMGFS start.......Not found!!!

anybody know if it can extract some file from a rom already cooked ???

thank in advance