For RF I'd suggest setting two boxes up in IR, getting them to work separately, THEN converting each to RF. I'd also suggest calling their support folks.
I tried it, it doesn't work. Trust me if you go to turn on DirecTV RF you can only use it on ONE unit and it assigns that RF code to EVERY DirecTV device so that you can't even use one RF and one IR. Please don't assume what I did and did not try and make me out to be some sort of liar. I tried everything possible with the remote to get RF to work on more than one unit and RF to work with another unit in IR, it's not possible.