12 GPU rig... but how???

In this discussion: https://bitcointalk.org/index.php?topic=1541084.msg19319534#msg19319534

There is an example and a tiny bit of talk about a rig that controls 12 GPUs

The idea is that the builder uses PCIe Switches for 9 of the cards and the other three are on board:

Using common MSI Z270-A Pro + Celeron G3900 + 4GB RAM +3 x PCI-E Switches (9 GPU's connected to switch and 3 GPU direct to motherboard). Power Subsystem - two HP common slot PSU 1200W + 160W Pico PSU (for motherboard and switches)
Sorry for bad photo and my English)
http://i.piccy.info/i9/8ec902e393a819cd6e28da0c657ce61b/1496350066/143938/1150706/_A5855D8E973CE290DECE4AFFBDA4CD5B935F4D51AF5C4080C2_pimgpsh_fullsize_distr.jpg

Does anyone have experience making the CPU / bios / whatever to detect 12... or maybe 18 GPU's?

TIA!