The DirecTV Gemini Air (P21KW-500) is pretty much a Google TV box. The remote is bluetooth and the little dongle has no IR sensor. So no way for the MX790 to control it.

I don't know if URC TC has a way to control it via IP. But that would be a big step-up in price over the MX790.

Also don't know if some of the other brand remotes that have come out, that do bluetooth control, can in fact control this box. It is based on the app 'Android Remote' so it maybe possible with some of the others. Just not URC.