I don't understand the "trust" idea about the live band...if Akagi Rie isn't "trusted" by YK for lives, then why has she been a special guest in the past, and why is she scheduled to appear in the upcoming concert? For that matter, why did Nozaki Masuke and Toudou Masahiko each play with Kajiura-sensei in several lives if, by assumption, she only "trusts" Satou Kyoichi or Konno Hitoshi as drummer and violinist respectively?
I can understand sticking to a band that's done well in the past, but I don't think that explains why Akagi doesn't perform with them. This is of course my opinion, since we have no explanation of the situation as yet, but I think it's monetary-related, given the fact that FJ is signed to Flying Dog, which is a smaller company than Sony. Not only that, but for all her popularity, I believe YK's live music in the form of FJ is a relative "niche genre" in Japan, as opposed to Kalafina, which has been heavily marketed by Sony lately. So to me, it only makes sense that Flying Dog would choose not to spend a particularly large amount of money on FJ lives - as much of a shame as it is, they most likely figure that Kalafina will beat them at every turn and the money for regular flutists/cellists/etc. will be wasted. (Of course, this doesn't explain why Kala has a similarly limited band, but I'm assuming the "trust" situation also doesn't apply to Kala's case, given the fact that they have performed with quite a few more musicians than FJ. A good example of that is in the Progressive tour, which had a completely different band right down to the guitarist.)