From what I could gather in chinese from Chuwi’s forum and in russian from 4pda the duaboot 64-bit bios can be flashed with an SPI programmer, many russian users on 4pda say it is the only way to flash it with this bios and user @Vedran also confirmed it on this forum.
I’m talking about this bios, for devices manufactured in 1511 with a serial number higher than 2000. DOWNLOAD
Disclaimer: I never said I have a dualboot device, just that my singleboot tablet is running a dualboot bios – there is no Android on my Hi8 Pro. Title could be misleading.