So it is possible to boot the MiniX into Fastboot mode, for much easier flashing of signed firmware files (update.zip cannot be flashed directly like in Clockworkmod Recovery). Remember that in fastboot mode, there is no AV out like on other smartphones that have an LCD.
Enter fastboot via ADB, see below.
The only proper way to exit fastboot on the MiniX is typing “fastboot reboot” (without the quotes). Don’t do “fastboot continue” that didn’t work for me.
Additional commands in ADB to reboot:
$ adb shell echo -n boot-fastboot | busybox dd of=/dev/block/nandf count=1 conv=sync; sync; reboot
$ adb shell echo -n boot-recovery | busybox dd of=/dev/block/nandf count=1 conv=sync; sync; reboot