The FSB's used for the audio in Halo Reach and Halo 3 all have a .info companion file that contains full file paths for audio contained in the FSB.
https://drive.google.com/file/d/1Z98XIJfBZcQ1_Y9IYkj98PiHXqPQPIYR/view?usp=sharing This is the English VO bank from Reach.
The FSB files themselves seem to just be completely normal, no adjustments to the format...so it's really just a matter of figuring out how to pair the full path names to the data in the FSB and extracting the files with those paths.