Had a similar problem with the earlier version of this product [FW-7551a-SV1] when trying to boot from the -serial image. Just went unrecognized. The -nano image written to a USB stick did however boot. The BIOS in the 7551 includes "UEFI" in it's name but surprisingly neither the SSD (SATA3 in this case) and the CF card in the case were EFI/GPT partitioned. YMMV
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