That thread only has a link to a modified
recovery firmware and nothing more, it says
Antminer S9k
Unlocked SD image. Unlocks SSH and Disables Signature Checking. Nothing more was done to the image. To be applied using a SD card.
OP, there is no custom firmware for the S9k, and these gears are pretty low quality, I would not attempt to change any settings on them, if anything, you should be looking to underclock them.
most s9k suck really bad.
I had four of them they all run hot and under-clocking was next to impossible .
I was able to run three with the middle board not attached.
they are very stable and do the two boards at a solid 9th.
In fact they are mining on mmpool.org