Best connection from Academy for International Business Officials to downtown Beijing and return?

Well, where do you refer to by downtown area?
Anyway, take Wangfujing Avenue as an example, you can take bus no. 905 (Inter-zone Bus), get off at Tiantongyuan North Station. Then take subway line 5 to get to Dongdan Station, Exit A. After that, walk west along East Changan Street around 750 yards. The return way is the same.

Or you can take a taxi from the academy to the destination directly. For the single trip, the cab fare is CNY 100 to 110 in the day time. This is the easiest transportation for you to choose.