A few thoughts I have are the audio commentaries on the Definitive Collection LaserDisc (available on the Dr Gonzo DVD release) and the 2004 DVD commentary.
This site has fan-made commentaries to play alongside the actual film soundtrack but I cannot vouch for how good they are. All 6 films are covered and they are timed to synchronise with PAL versions of the films.
Other options include the Radio Drama's which are very good and descriptive and the Story of albums too. These are only available for Eps 4, 5 and 6 and are "out there" in mp3 form to be downloaded.
Good luck in your quest and I look forward to hearing how you get on.
Finally, welcome to the forum. Hopefully you can stick around and enjoy the fun and games we all have here.........