S9 , S9k , S9i , Sk , S9E each of these have different "looking" hash boards, I am not sure about the structure design and current flow but these are different from one another when you simply look at them with your bare eye, in fact even the S9 itself has 2 different hash boards.
But as far as Chips are cornered, here is how they are grouped.
S9 and S9i > same chip
S9j > own chip
S9k > own chip
S9E > own chip
as for the last two , someone mentioned that both have the same chips, but I am not sure, the boards look completely different, heat sinks on the S9E look fairly large , which makes me think the chips are different , unfortunately the last two models are pretty new to the market and I doubt anyone has gone to the extent of changing a chip on them.
Talk about design, I got something for you.
The above diagram explains how the signal follow within the hash board, it should give you a better and simpler understanding , if you have problem determining what the colors stand for, feel free to ask and I would explain.