I currently have it running 12 gpus. I didn't need to change anything in the bios, however sometimes when it crashes and i do a power cycle, it will not boot up.
I'm able to get it to boot by turning off half the rig to get into bios, and disable csm compatability (uefi only, no legacy). For some reason that setting gets toggled sometimes when the rig crashes.
HTH!
What GPUs did you has?
You are a lucky man!

10x rx5700 and 2x radeon vii. I have the same cpu and ram amount as you.
also try different pcie speeds, mine are set to 2x