It seems Tobi RX does not work with the EyeX SDK at all. When I saw the following information, I was hopeful but unfortunately it is not applicable.
“In order to use the EyeX Engine with a Tobii REX eye tracker you need to install REX device drivers.”
I will try the Gaze SDK to see if that works with the Tobii REX. If it does not, I will start looking for a more reliable alternative product from another vendor.