That's very strange because I have the pkg file from which I extracted the fpg file.
And the pkg file runs in RPCS3 emulator just fine. (https://rpcs3.net
UPDATE: I successfully extracted the files with offzip, and now I'm converting sg2 texture files to png and see what I'll get. Thank you very much!
UPDATE2: Even if I successfully extracted the files with offzip, they are the same files repeated over and over and no new information was extracted that was already extracted by the flog_x360.fpg.bms script. So it's seems to me it's a protection of some kind because any character sprites or stage sprites or sounds/music cannot be extracted, just portraits, misc ui textures, texts, fonts and some hit sparks.
Can you analyze further this format because I don't think this archive is corrupted or old version just a protection.