I know it's not officially supported, but it is possible, but how do you do it?
 

Can you not just use the Older SLI Bridges?
BTW, Really Nice Scores you have
 
You may want to PM sam nelson he is very good on 4-Way SLI.

From what I have heard you have to...
 
#1 Have the correct sli bridge. Such as 100-3W-0032-LR for 3-way, or 100-4w-0042-LR for 4-way. Bridges without metal contact points won't work from what I have heard.
#2 Enable sli inside the nvidia control panel.
#3 Download nvidia inspector 1.9.7.8, and open the profile inspector that is included with it.
#4 Make sure you have the profile  _global_driver_profile (base profile) selected.
#5 Click the button "show unknown settings from nvidia predefined profiles" to show all hidden profiles.
#6 Scroll down the settings list until you find the section listed as SLI, and change the following settings...
- "number of gpus to use on sli rendering mode" to 3 or 4 depending on how many gpus you want to run.
- "nvidia predefined number of gpus to use on sli render mode" to 3 or 4 depending on how many gpus you want to run.
- "nvidia predefined number of gpus to use on sli render mode on directx 10" to 3 or 4 depending on how many gpus you want to run.
#7 Scroll down the settings list again until you find the section listed as unknown, and change the setting 0x10FD4C5F (7 profiles) to use 0x01F296C1. Scroll down more and change the setting 0x209FD306 (27 profiles) to use 0x0FC00008.
#8 Click apply changes and your done.
 
I also heard you might need to do the same for each game profile you're trying to run in sli if adjusting the base profile doesn't work. You may also need to set only 0x01F296C1, or 0x0FC00008, but sometimes you may need to set both under each individual profile.

Maybe time for you to get two more EVGA GeForce GTX 1080 Ti K|NGP|N
This way you can update your How To Page with SLI How To.

bcavnaugh
Maybe time for you to get two more EVGA GeForce GTX 1080 Ti K|NGP|N
This way you can update your How To Page with SLI How To.

I'll be sticking with 2-way from here on out as newer games are getting away from using 3 & 4 way.

WOW!

Sajin
From what I have heard you have to...
 
#1 Have the correct sli bridge. Such as 100-3W-0032-LR for 3-way, or 100-4w-0042-LR for 4-way. Bridges without metal contact points won't work from what I have heard.
#2 Enable sli inside the nvidia control panel.
#3 Download the latest version of nvidia inspector, and open the profile inspector.
#4 Make sure you have the profile  _global_driver_profile (base profile) selected.
#5 Click the button "show unknown settings from nvidia predefined profiles" to show all hidden profiles.
#6 Scroll down the settings list until you find the section listed as SLI, and change the setting "number of gpus to use on sli rendering mode" to 3 or 4 depending on how many gpus you want to run.
#7 Scroll down the settings list again until you find the section listed as unknown, and change the setting 0x10FD4C5F (7 profiles) to use 0x01F296C1. Scroll down more and change the setting 0x209FD306 (27 profiles) to use 0x0FC00008.
#8 Click apply changes and your done.
 
I also heard you might need to do the same for each game profile you're trying to run in sli if adjusting the base profile doesn't work. You may also need to set only 0x01F296C1, or 0x0FC00008, but sometimes you may need to set both under each individual profile.

Tried that route, unfortunately there is more to it.  Even with that, GPUz still only shows 2x SLI enabled.

https://www.youtube.com/watch?v=eyJyKtTt1rY  This Russian youtuber said he only had to enable SLI in the Nvidia control panel, and nothing more.  You also need a correct tri-sli bridge, as no every single one will work properly.

Still going nuts with the GPUs huh Gunslinger?
 
One thing to check is your motherboard and more specifically it's PCi-E lanes available. I know some boards pull PCI-E lanes away from the slots when certain configurations of NVMe SSD's are used and in what ports they are used in. It may be pulling 4X lanes away from a PCI-E slot and as such SLI will not work as I'm sure you know SLI requires a minimum of PCI-E 8X to run.