Armed with the new insights of how the installation tool actually works, I now have a working eMMC+NVME system. I could not get SPI to work. It pretended to accept being written to, but didn't. Considering how slow SPI is, I wonder if an eMMC+NVME system boots up a little faster. For now, I'm working on getting the HDMI sound working, and hoping for a fix to the death-loop-boot issue solved by an extra dumb 5V power cube. I'd also like to get rid of the extra Wi-Fi device that keeps throwing activation errors.
I appreciate all the hard work developers have to do get software going smoothly. It's not easy.
Bye.