Hi @ev23, thanks for your query.
I am afraid that the Tobii Unity SDK plugin will not work with the x2-60 as this is a UPD (Network) Based eye tracker.
For now, the only eye trackers that are officially supported with the Unity SDK are the Tobii 4C and EyeX.
Tobii Pro trackers that can operate via USB such as x2-30 or X3-120 may work with Unity although this setup has not been extensively tested.
My apologies for the disappointing news, please let us know if we can be of any further assistance.