thanks Jonas_OMI
At least one way to process raw EEG-Data must exist, either a third-party tool like openvibe, or you must write a custom interface for acquisition, which is in someway obsolete, because Openvibe (based mainly on python) is powerful to calculate any kind of parameter or can be fully integrated into own software chains (because open-source) to run in the background and to pass-through signals with a minimum of preprocessing.
We can recommend it, because it is free and provides an incredible amount of inter-compatibility of hardware inputs and outgoing data streams, including LSL.
If you are interested in doing some simple signal-processing within Unreal Engine 4, you can take a look at our Signal- and Data-Processing Plugin that features Interactive Real-Time Visualization within your game