Another member(he can reveal himself if he wants to) and I were contacted by a Chinese manufacturer who did something almost identical to what you are trying to archive, they made their own hash boards which were more efficient than the regular S9 hash boards, and their own firmware which you had to deploy on the default controller of the S9 (the hash boards won't work with the default firmware).

The company wanted economical consultation in terms of pricing, I contacted a few major resellers in China, Russia, and the U.S, and sadly the final sale price was not tempting enough to convince anyone to get those hash boards, mind you the company that did this is located in china, and they paid us just for the consultation, they clearly had the money and the manpower needed for that job, and the results were not so great.

I am not aware of where did they go wrong or how difficult it was, but I am certain they had more skills, money, and resources than you do, which is one of the main reasons why I told you in my first comment that this "won't work", it wasn't a blind baseless statement, I hope the above information will be beneficial to you oneway or the other.

Good luck.