Only using the Foxsat that originally recorded the content. The encryption key is unique to the box.
If you add non freesat channels, go into non-freesat mode and reboot. Then manually initiated HD recordings aren’t encrypted. If you rename the .ts (to get rid of some weird characters) then most media players/computers/tablets will play them back.
Do you know whether the encryption key is held on a chip? If so, is it possible to remove the chip and put it in a new Humax machine?
Not a clue, afaik what you suggest is not possible. these days chips are soldered onto motherboards, often with double sided tracks. I doubt you could get one off without ruining the motherboard and chip.