Onyx International says they no longer have the firmware.
Anyway, i managed to install the latest firmware from onyx-boox.com. Turns out that for the M91S , you need to put the extracted .UPX file on the SD card instead of the ZIP.
The firmware was installed succesfully. It changed the image on the splash screen. Unfortunately, the device still doesn't complete the boot process. The progress bar fills, and then nothing happens anymore.
