pretty straight forward.

connect to both gizmos:

1. light
2. camera
3. shadow casting geo
4. shadow receiving geo

the shadow 3D gizmo will give you a shadow pass for multiplying or grading the image. following knobs exist on this gizmo:

1. Light Type: You can choose the light type. Parallel/direct or point/spotlight.
2. Shadow Quality: The shadow quality is essentially the focal length of the shadow projection camera. higher values give smoother results. but too high values cuts the edges of shadows. really low numbers are needed especially when set to orthogonal (down to 0.2).
   
3. Scanline Samples: adjusts the scanline renderer that renders the shadow pass
4. finally you can choose disable to get the full shadow with the parts that get occluded by the shadow casting object himself

the RenderBoth gizmo needs the same inputs and simply renders both geometries for multiplying (or getting graded) with the shadow pass.

additional settings of the used scanline renderers will be implemented.

dunno if this could be of any use for someone else.