This is super cool that you're figuring this stuff out! Thanks so much for poking at this!

Do you think that the caching issue is inherent to that brand of SSD, and that we simply should pick a different brand if we want EmpegUpgrade.exe to work with it?

I'm not sure if the older problems (the ones we worked through in that older thread, on that older KingSpec drive) were the same problems or not. But somehow you were able to work through it, and now I have a drive that's working really well in the empeg, thanks to your help. So there's certainly a solution to be had here, even if it involves issuing a lot of console commands. I'm glad you've found the root cause!