C o m p o s i t i n g

Shadows for 3D Objects rendered in LW/Max

For static objects, you can place them in WCS and select Shadows Only (General page) and Cast shadows (Shadows page) in the 3D Object Editor. As long as a Shadow component is enabled for the terrain to receive shadows from 3D Objects and the Render Options have 3D Object Shadows enabled, you'll get shadows but no 3DOs.

For objects animated in LW/Max, shadows need to be cast there. Use the DEM objects exported from WCS to catch shadows.

Z-buffer compositing and 3D volumetrics

Whether this works depends on how you achieve the effect. Many volumetric filters in LightWave (Hypervoxels, for example) are not true geometry, so they may not take z-buffer data into account. Try an Atmosphere in WCS/VNS, especially the new volumetric flavors. Haven't tried this yet with the new WCS6x/VNS2x compositing feature.