I was able to work out the shader fixes and now I can show you a good schematic of how the new lighting system works. Instead of a single light source, we now have three types of lighting that are combined for the final render. Direct lighting is the standard deferred lighting model you know and love from Leadwerks. This looks great, but shadowed areas have always looked pretty flat.

The second component is the new GI ambient lighting. This is a view-independent lookup on the local cubemap that gives us a rough approximation of single-bounce radiosity. Notice how the lightened areas are lit up as a result of the direct lighting in the previous image. The bluish rectangle on the floor is a result of the sky color reflecting from above:

Finally, we have the new specular reflections, a high-res dramatic reflective effect that changes with the view position:

When all three lighting contributions are combined, it looks like this:

And when you add textures, it looks like this:

Instead of like this: