I'm trying to do the same.
i paid and downloaded from upgrademyaudi and followed the instructions.
i copied over to the sd card fat32 formatted and it would not read.
I got the lastest form HN+R and would still not read.
does the firmware need to run first and then maps.
i'm also very cautious as i dont want to brick the unit.
has anyone used the builds and guides from upgrademyaudi, if so some assistance and advice would be greatly appreciated.