I am studying the differences between these units too because I have recently acquired an AU-D707X Decade and I want to learn as much as possible about it. So I appreciate this thread. I observed some differences and also noticed that there are less adjustments points in the AU-D707X types. Notice that the AU-D11II and the AU-G90X have two different rails for the power amplifier which are used to drive speakers in two impedance ranges.The quality of the chasis for the AU-D11 is also better than that for the AU-D707X.
This thread is relevant. Please see Page 5 there.
I agree with what John said. The AU-D11II is a special unit that combines characteristics that are present in several similar units (AU-G90X, AU-D707X and AU-D77X). It seems like Sansui combined the best of all of these in the AU-D11II.
I think that to repair the AU-D707X one needs a combination of manuals like that for the AU-G90X and that for the AU-D11II.