I actually tried one of those USB video cards in the past and it didn't do anything unfortunately
However, I did try something suggested here and got a "result", I put an eyepatch over my right eye, and have been using my setup, and so far (it's only been 30 min or so) I haven't had symptoms. I have been hypothesizing recently based on my experience that my issue seems to be binocular focusing related. The muscle pain I am feeling feels like the pain I get when I have an improper prescription contact lens or glasses, and it feels like the muscles in my head are trying to "move" my eye to compensate, resulting in those muscles tightening up which then impinges nerves and causes migraine (according to my nuerologist)
I'm going to continue wearing an eyepatch when using that system for a couple hours, and if it holds up, that would seem to at least indicate a root cause to the problem: Somehow the way the Windows 10 desktop compositor is rendering the image, regardless of video card or monitor, is causing my eyes to struggle to maintain a binocular balance between the two eyes, and the compensation of that is what is causing my pain. I have no idea how that would be fixed, but at least it is a plausible hypothesis to start from.
I'm going to start a new thread to see if other folks have had the same issue