I was aware of the Tokyo Grain Exchange, volume there is very low however. I'm pretty much looking to see what is having so much influence on the CBOT prices in the overnight. Volume seems to pick up significantly around 6 and 7cst. I'll take a look at the others.
None of the exchanges you listed appear to have any significant volume. It looks like it must be the Dalian Exchange that is moving the soybean market in the overnight. Unfortunately I don't see any way to gain access to that market.
I think you are right. My broker once told me about a guy who came back to the office specifically for the "Chinese grain open" in Dalian and Zhengzhou.