Oh, that's interesting - I had (wrongly) assumed they would have encrypted or "password" protected the content by locking it to the original card. Neat that you can view content. I had my own box, and bought a s/h box (because a client was looking at options for a static caravan they own), but when I cancelled Sky (and indeed TV Licence too) decided I'd re-use the hard drive. I actually downgraded the viewing card (so it might work when next I buy a licence), but found it very difficult to extract the hard drive (the box I have has quite an awkward to remove metal box around the hard drive). Sorry for going off at a tangent - I suppose they considered they'd get more complaints if they locked the recordings to a card and then nothing was viewable if they had to send out a new card...
Anyway, good luck with getting something to record. I hope redgate comes back and explains their method. From what I've read, the recording would probably need to be via a SCART cable - HDMI is intended as encrypted (to prevent high quality copying) and only unit with an HDMI input is the TV (OK, AV Amps may include HDMI inputs but don't themselves do recordings - recording boxes don't have HDMI input)