At the moment there is no built-in support for multiple eye trackers in the EyeX Engine. As you said, it is possible with the Gaze SDK (as long are the eye trackers have different URL:s). So technically it is possible to add it in the EyeX Engine as well, we just need to prioritize it. Add a feature request in the Feature Requests forum and we’ll see if there are many others who require multi-tracker support.