All Antminers S7 working perfect with any B.B.B. from S5 antminer.
And S5 miners can buy a lot cheaper than your toy.
We need controller for S9 , S7 is history.
Just got my 2 new s9 batch 11's: Looks like Bitmain has dropped using a BB per-se. Ref my post
https://bitcointalk.org/index.php?topic=1493601.msg15975363#msg15975363edit: However, if one has some of the original s7/s9 IO boards around then of course would still be nice to be able to 2nd source BB's for them