The receiver only reads FAT16 or FAT32 formats. It will not recognize NTFS or exFAT.
Ensure the firmware files are not hidden inside a folder. They must be in the "root" (main) area of the drive. denon avrx520bt firmware update top
Because this model is "offline," you must download the update from the official Denon support portal on a computer. The receiver only reads FAT16 or FAT32 formats
Press and hold the and Preset Ch + buttons on the main unit simultaneously. The display should read "Update Starts." denon avrx520bt firmware update top