Years on I stumbled across some guy on a Russian forum that had his running Rockbox. I decided I wanted to try the same, and eventually managed to get it working.
It's been a few years, so the memory is a little foggy. But I remember it requiring a Windows 7 system to run a weird ass Chinese software to flash a modded bootloader onto the player in order to make it boot from the MicroSD card slot rather than the built in flash. I then stuffed a modded version of Rockbox onto a memory card and slapped that in. Everything works just like it should, apart from the onboard flash. I suspect that has just been replaced with the card slot in the bootloader.
Since it's a very FLAC-y kind of player that didn't matter much though, because the onboard flash is only 16GB. I ran a 32GB card in it for a good while, but just for fun I just picked up a 256GB card for it, and it works great! iirc. the officially supported highest capacity is 32GB, but it doesn't seem to mind at all.
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