I've got one that is submerged in mineral oil with a pump loop & silent fans.. It's literally silent.
I really should plug it back in...
Do you have any photos for the setup? i imagine it is a DIY setup and not some plug-and-play box?
You can even without firmware update remove 1 board with chips and reduce power consumption.
On the S9, the efficiency you get using custom firmware is very noticeabl, since both Vnish and BO+ tune each chip individually, while on the stock, the best you can do is set a differenf frequency and voltage for an entire board.
Ofcourse, the good thing about stock firmwork is that you don't any fee.