A:Answer You might have to use an IR blaster from the hub for each unit, and light-shield each unit/blaster combo from one another and from the hub (e.g., by putting them inside separate cabinets or well-ventilated boxes). Seems pretty cumbersome.
Even then, I think you'll have trouble controlling the newer DirecTV models (Genie 2). DirecTV does not support 3rd-party universal remotes, like the Harmony.