Hi, Xeffects renders a shadow map from one light only to produce shadows, so extra lights will not affect shadows.
You can render multiple shadow maps, and altering the code to do this is relatively easy.
Frame rates will drop though, as every etra light requires a complete redraw of each scene.
You´ll need to re-render the depth map, calling the same code but using a different light, then change the shader to look-up the depth value from both depth maps. The code is easy enough to follow if you´ve experience with this sort of thing, if not, it will take you a good few hours of digging, thinking and research on the principles.
Behaviour with different drivers is normal because the code has not been exhaustively tested for all drivers.
Probably the binary was compiled from different code changes, hence different functionality.
In any case, XEffects is easy enough to follow although it will take some time to go through, once you have done that, you will be able to make the changes you need in future easily.
No pain, no gain as they say!