Well, that's the problem, really - as I don't have 300/600/700, I can't try it and then provide a proper guide.
I think it should be possible to extract just a flasher from those russian links I provided and then use the "build new image" - "flash image" method of Igorsk's flasher (rather than the "copy image from card" - "flash image" expected by the russian guides).
Updating your original firmware (with cramfs tools) will be difficult because the firmware is encrypted.
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