Can't boot with 2 displays with CSM disabled?

I've got 2 monitors attached to a GTX 1060 with an Intel iGPU configured in headless mode. Since Nvidia is no longer formally supported, I am still running High Sierra, 10.13.6.

I was never able to get my hack to boot properly without enabling CSM support in BIOS. However, I discovered that it was able to boot fine if I only had one monitor attached. After that I could reattached the second monitor and everything would be fine. I can't find any information about this issue beyond a note in the WhateverGreen documentation:

Support for 2 or more displays on Intel Skylake and newer desktops is missing or buggy. In macOS 10.14.x there is an improvement tendency.

I'm not sure if that note applies to my situation, since I'm mainly using a dGPU, but it might suggest that I'm SoL. Has there been a workaround for this problem, either a setting to configure in opencore or a patch for whatevergreen? To clarify, it boots fine with CSM enabled, so I can just keep it on if there's no solution.

Here's my Config, hack info is below:

Z170X-UD3
Skylake 6600k
GTX 1060
MacOS 10.13.6
Model: 17,1
Opencore 6.8
All kexts up to date

submitted by /u/ritzbitz00
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