I'm not familiar enough with the HR-21's output capabilities to comment, but I can tell you a few things.
First, cable companies are required to provide a IEEE 1394 (Firewire) output on all the STBs they provide, to allow subscribers to off-load content (presumably to computers). It is a bit tricky to get it to work, because IEEE 1394 is a tricky thing to get working.
However, if you know a good bit about computers, you can probably figure it out if you spend enough time researching it.
However, though these boxes must support IEEE 1394
output, none of these boxes support putting content back
in. It is a one-way door.
I'm not sure if the HR-21 has the same type of output, but I'm relatively sure that even if it does, it does not have a means of restoring recordings off-loaded in this manner back onto the
DVR. Again, it's one-way.... out.
DVR hard drive space is a major point of value. The general viewer doesn't save up as much content as you do, so the general offerings don't include ways to store more than the certain amount. You could, I suppose, get a second
DVR. Also there are options for upgrading the storage for your HR-21 though:
HR20, HR21, and HR22 DirecTV HD DVR Upgrades
