Initially, I wrote Axis-Aligned Bounding Box code for every primitive, and then wrote methods to convert these between spaces (MCS AABB -> WCS OBB -> WCS AABB).

Then I wrote code to create the Voxels, determine which voxels contained the WCS AABB of each primitive, and then I wrote a 3D-DDA style Voxel traversal algorithm based on the paper
"A Fast Voxel Traversal Algorithm for Ray Tracing" [Amanatides, Woo 1987].

The initial results were pretty good for primitive scenes with a grid of spheres or a grid of cubes. Meshes though could be improved, and later on I will discuss this.

Naive Method: 279 seconds.
Uniform Spatial Subdivisions: 128 seconds.

Naive Method: 25 seconds.
Uniform Spatial Subdivisions: 10 seconds.