A clarification of that puzzling last line from Chapter 400 now that Sleepyfans scan is out and so is Cnet's translation. The first translation we had from mangastream gave everyone the impression that the hougyoku had some sort of sentient will and was taking Aizen over or something (Aizen: "It seems that at long last my soul has begun to understand the will of the hougyoku"). Nope, got that backwards.
Aizen: It appears that the Hogyoku has finally begun to understand my heart.
Aizen: It would seem that the will of the Hougyoku... // ...has finally begun to understand what I desire.
czeliate explains in this post at BA
So, yes, this all makes more sense--Aizen is in control of the hougyoku instead of the other way around! Just wanted to put to rest some of those braincells out there that were hurting themselves with speculation.