Yea, the "6000 songs parade" documentary is pretty great. Not that the few full others that we got weren't (7rules, "Music of SAO", the ancient MBS one)... Like I said at some other time, I really would love for YK to release a "YK ARCHIVES" bluray for some anniversary, compiling whatever documentaries & interviews they could salvage. Plus, random live videos that they have. Reach out to TV stations while they still can help.
Going back to this particular discussion though, I would also recommend looking at the knk3 demos that we got during ufotable's livestreams as a probable insight into what Kajiura submits to the studio before recording sessions.