I am not sure what else to try. On the HD-FOX (which looks similar to your model and has a plug in USB drive, but is for terrestrial TV rather than satellite) all recordings are encrypted by default (standard and high definition) and the high def. content also is also flagged as 'enc'. On the standard HD-FOX this flag has no function. On the HDR-FOX (like the HD-FOX, but with an internal hard drive) if you copy a standard definition recording to a USB drive using the device's remote control, the recording is decrypted in the process. A high definition programme is only decrypted if the HMT file is first modified as described in post #8 (for example), otherwise it is copied but remains encrypted. The HD-FOX allows you to move a recording but not copy it. The HD-FOX with customised firmware can run the HDR-FOX software and this is how files are decrypted.
With your model do you get an 'enc' flag next to the on screen title with high definition recordings? Does your model allow copying from the USB hard drive to a second USB drive? Are standard definition recordings encrypted by default? Do you have to copy standard definition programmes to a second drive using the device's remote control to get a decrypted copy?
It may be the case that modifying the HMT file does not allow the recording to be decrypted.