I'm pretty sure DirecTV should be able to set you up with 2, dual HD DVR receivers.
I recently got an upgrade to a Dual HD DVR for my new living room TV.
I put my old dual DVR receiver (not HD) in the bed room, and moved the bedroom basic box (also not HD) to my computer room.
That's 5 feeds, 2 HD, 3 Standard definition , running off a new (single) 5 LNB dish.
I think DirecTV can what you want and off of one dish. It might have to be a new dish, but I believe they can do it.
I could be wrong.
They do have a Dual HD DVR. But it has one draw back. As far as I can tell (since I've had it, only 3 days). You can't "buffer" rewindable veiwing for each "feed". Infact you can't even switch to find the other feed. It only exists when you engage a recording and want to watch another program, or want to record 2 programs. It's as if it's not there when not doing one of those two things.
My previous Dual (none HD) DVRs would buffer on ether feed, and either feed could be accessed.
Just a heads up about the DIrecTV equipment.
Some one will chime in soon with a wealth of much more accurate information.
But since I just had it done, I'm thinking if they can set me up the way I described, I think they can certainly accomidate 2 HD DVRs. Even if both have dual DVRs in them. I'd be very surprised if they gave you a flat out no, that it couldn't be done.
Worst case scenario is that you will need two dishes.