Onto flashing. In the user interface, there is an 'upgrade' feature (similar to regular router flashing procedure) that can allow you to flash a firmware image from a USB. So I copied the extracted image to a USB flash drive, rename the extension to bin (it didn't recognize img).
However, when I try to flash the image, it accepts it, but then it immediately reboots, with the stock firmware intact as if nothing happened. Here is a video on how it looks like: https://streamable.com/oq84hn.
I have tried doing it multiple times, but the issue keeps persisting. This is presumably a safety/security feature to reject 'corrupted' images. How would I bypass it?
Somehow, someone with the hardware on their desk will have to reverse engineer the OEM firmware format for that - and you definitely want a failsafe (working serial console, bootloader access and OEM bootlogs and ideally even a root shell) before even thinking about trying that - and yes, this someone will be either you or noone. Maybe this hypothetical someone can make the process easier for others in the future, maybe not. x86 does not necessarily mean generic or unlocked hardware, especially if android, chromeos, windows ce or windows embedded are involved.
Without serial console access, you're flying blind and don't know what's happening behind the scene - and any, even minor, mistake is likely to be your last one with this hardware.
No, this type of connector for a serial connection is no standard.
But i know at least two devices, who are using this kind of 3,5mm connector for data transmission. Unfortunately, the pinout is different on both these devices.
Of course not...an audio output isn't the same as a serial data connection.
So, what do you need: A serial connection to your Mac, either an old-fashioned RS-232 (if such a connector is still available on them, but i think it's not) or an USB-Serial-Converter. The easiest way is to try to get the original data cable. If you can't get it, or at least the wiring of it, you'll have to make one of your own.
If you have some basic skills on electronics, you might be able to measure which of the 3 rings on the 3,5mm plug is Gnd.
Then you have to solder an adaptor from your (most likely) DB9 to a 3,5mm plug. Maybe you even need a so-called Null modem adaptor, so the Mac will receive the data. To find out which of the remaining 2 rings is Transmit Data and Receive Data, is best done by trial-and-error.
If this is already to complicated for you, you might look for someone who will do this task for you or you just put the receiver in the recycling bin...
Because: Even with a working serial connection between the receiver and your Mac, you still don't know if the receiver will even send any useful data when powered up.
If these obstacles doesn't scare you off, than good luck with it.
On any question that will surely arise, i'll be trying to give a useful answer.
That is not an x86 processor. There are SoCs specific to these cheap TV boxes. The Rise MP6 was intended as a desktop processor and requires a large supporting chipset in order to run. Of course HDMI did not exist back in that day either.
The TV boxes run a non-Linux OS in order to fit into the very small memory space they have. The flash chip is probably only 4 MB. Because of the small memory, there has not been much development toward running a general-purpose OS on this sort of hardware.