The Edge Blending module does not allow you to specify which outputs of the TripleHead2Go are used for the blend.
You can use just two outputs of the TH2G (left and right), but the center output would be unused. You would be configuring the TripleHead2Go as a DualHead2Go.
The module works as a 2x1 or 3x1, but it does not work as 2x1 + 1. In order to use Edge Blending plus additional screens, you would need to have two computers running ProPresenter or look into using PVP2 or PVP3 along with ProPresenter.