Trying to flash Mayalsk update.img via GPS SD, not working / no recovery

I've bought an Android 6.2" HU with 4.4.4 and Quadcore 1.6ghz, 1gb ram, 16gb nand.
Google/Ebay search for Pure-Google-Android-6-2-Double-2 Din-Car-GPS-DVD-Player-Radio-Bluetooth-Camera

It's not branded. The vendor sent me a firmware for "AD-UN6202". MCU is TS901.151104. That's about what I know.

The firmware from the vendor is a bunch of files. The HU reads and flashes these just fine, when using GPS SD and reset. Files are:
root.tar, ramdisk.gz, recovery.gz, atc.upd, target.bin, rd_datazone.bin, 83XX_Preloader_realchip_sd.bin, data.img.ext4, arm2.bin, cache.img.ext4, data4write.img.ext4, databk.img.ext4, u-boot.bin, uImage, system.img.ext4.

I wish to put on Malaysk 4.4.4 rom, but it's not reading the update.img which i've stored on GPS SD. I've tried a bunch of different methods to get into recovery, to no availability.
So how to I proceed?

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