Matuus, our in-house Guru3D NVHardpage programmer stumbled into the same issue I had as well. The NVIDIA PhysX driver once install will activate itself on the GPU, and can not be disabled.
This little NV PhysX Tweaker tool will allow you to actually choose to enable or disable the PhysX driver over the GPU and if preferred, the CPU. Very simple, yet very handy.
Download - click here