Regarding Tobii.GameIntegration.dll. This dll is our internal API that might change a lot in the future. That’s why it was never released standalone but only as part of Tobii Unity SDK. If you are using Unity the best would be to stick to the public api provided in TobiiAPI class.
If you are willing to run calibration inside Unity and you have an appropriate license for it, please send me pm and I will send you Tobii Unity SDK package with calibration sample. In that version Stream Engine calibration functions are reexported in Tobii.GameIntegration.dll and you don’t longer need to use two APIs in parallel.