Attached Link: http://www.thomaskrahn.com/Tutorials.The_making_of_Aragiaua.htm

Volumetric atmospheres don't give shafts of light (although I'm happy for someone to prove me wrong). Try using one large powerful volumetric spot place high above the scene (see Thomas Krahn's excellent tutorial on the above link). Personally I'd use multiple volumetric spots which is trickier but gives more control over the overall effect.

Cheers,
Mark