Does anyone here have experience with Game Extractor?

[gameripper]

I think the issue is that the game assets aren't named with file extensions

I repeat myself. GAME RIPPER scans for assets using magic bytes only, it also automatically adds proper file extensions on export (and what's more saves images as PNG files as well).
Not to mention that it would have chopped off that garbage before the BM header for you automatically.

I have one more question, hopefully. There's also some files that start with iMUS and ALSV, what would those files be?

Try List of file signatures or the "file" command under Linux/WSL, but probably some custom proprietary format.

Good luck finding a tool that can read these. Maybe ffmpeg or mpv worth a try (they are known to support some old and proprietary game formats too).