Understanding volumetric models in Three JS

I have been working with this volume rendering example and uploading my own models. I have worked primarily with meshes before so this has been a new avenue and I can’t seem to find too much info on volume rendering in three js. My models can contain voxels with many larges values and few voxels with smaller values. If I select mip rendering, then all the large values obscure the small values which will not be seen. Similarly, with iso threshold, if I set the threshold to the lowest, I can see all my voxels but the higher value voxels will obscure the lower value voxels. Raising the threshold will only show the higher value voxels. So I was trying to figure out how to properly display voxels in three js. I believe it would be very helpful to a user to visualize if they had the ability to provide a lower bound and upper bound threshold to display specific voxels values. But I am unsure how this is done and I also want to know where I can learn more about volume rendering in three js.