Thank you both for your helpful replies, which definitely add pieces to the puzzle!
RE USB burning tool and Android flashed to eMMC, IIUC that is what we would need TWRP for (which would actually also enable us to backup the pre-existing image on the eMMC for recovery later on, before even attempting to put other images on the hardware).
So in the case of your box, avin, that would be TWRP S905X3 (I don’t know if that exists, or if it does, where that should be found) and in the case of the VidSticks, it would be TWRP S905Y2 (which I also don’t know whether it exists or where it should be found if it does).
I do know that TWRP S905X2 exists - as per a tutorial here - but I don’t know whether it would also work on a S905Y2 box (which is supposed to be just a slightly stripped down version of S905X2, according to this spec and this thread)
vpeter, I imagine the thread to which you’re referring is this one, in which you also link to this one ?