However, I think this firmware ANTMINER-S9-all-201705031838-650M-user-Update2UBI-NF.tar.gz will work on s9i units.
In fact, I am certain it will work just fine, how do I know? I tried it before (I forgot that I had it in the previous post).
I do not want to advertise any custom firmware, but just so you know, the "overclocking" on the stock firmware isn't all that great when it comes to power consumption/temps, so if you are in a cold place and pay no power bills then the stock firmware is your best option because of the no-fee.
OP, thierry4wd is a trusted fellow miner here, you can use his modified version as well.