Square is really making me hate the fact I can't read Japanese. Also I CAN'T STOP MAKING THREADS.

In addition to the audio drama, there is a full-fledged novel that is written after X-2 and leads up to said audio drama. It's not even a short story like the FFVII stuff or FFXIII's Episode Zero, it's 200 some odd pages so you can forget even a fan translation coming out soon. Some vague discussion of it at the bottom of this page
Final Fantasy X-2.5 plot summary [This is a new Nojima novel, not the FFX-2 HD thing] - Page 15 - NeoGAF