I am finding the same issue. Did you find any support?
a desktop/laptop is able to do that since use of TV as a monitor is a grandfathered use. Currently you may also use a Roku device (some older models won't work) attached to an HDMI port on the projector. The Roku is currently on a free beta test.
So for all, i actually wound up putting a switch onto my set top box and put in a HDMI transmitter and receiver and it works perfectly. It was an expensive setup but it works very well. So now I am actually running a three switch setup so i can send the signal from my Xbox or set top box over to the projector as long as I am within 150ft of the transmitter.