you have to open the Box and search for the Nand or EMMC Flash, then figure out which pins you have to shorten to recover over USB OTG, the Mini M8S has also only full size USB, one of them has OTG.
See this for more informations http://freaktab.com/forum/tv-player-support/amlogic-based-tv-players/s905/tronsmart-ac/firmware-roms-tools-at/565449-running-linux-from-sd-card-or-usb-flash-drive-using-balbes150-method-and-files/page13
