Hi,
I'm currently studying Japanese in the AMES department so hopefully I can offer you some advice or at least information.
The AMES course is quite small and so where you apply and your interview are extremely important in getting in; I was pooled and reinterviewed before being accepted. I've heard that some directors of study are particularly fussy when it comes to AMES, or they just disagree with the department. If you apply to a college that does not have a Dos in your subject it is far more likely you will be rejected or pooled as they won't know what to do with you.
In terms of your application, it sounds like you did really well, so I wouldn't panic about your grades - I got AABBB at AS level, so I'm sure that's not an obstacle. Improving your application sounds like good idea, they like the EPQ as it gives you something to talk about and having a passion for your subject, particularly fleshing out the history side as you seem to be more of a linguist is important. They also look (strangely) for resilient candidates as it is a tough and very fast paced course, so if you do decide to reapply you may want to put that across.
Regarding SOAS, my offer was the same, AAB, which I think is great for such a specialist university - it was certainly my second choice, however I can't give you much perspective as I don't go there. They do do tours on Wednesdays (if I remember correctly) so it may be worth checking it out if you haven't already
I can tell you a bit about the Chinese course as I do speak to them quite regularly during term time and we share the history course.
Feel free to message me with any questions
Sorry about your application, sounds like you were unlucky really