Noesis is better for extracting data from FFIX because it adds file extensions, and things can be read directly from Noesis.
I have had some experience with IX sound effects myself, where I replaced one sound file for another (of an identical size) in the disc image. I believe they were AKAO files, so I presume identical to VII's sound.
This might be relevant. But I assume there's no converter/direct player for it.