I've been meaning to come back to this, but have been working full time on stuff that pays the bills
Here's some gifs that I actually produced months ago. Most of the lighting in the scene is from a cube-map, with a few (green) dynamic lights in there too. There's no shadows, so the "SSSVRT" adds all of the shadowing seen in the odd frames of the gifs:
Seems to work really well on shiny env-map-lit (IBL) objects to 'ground' them.
Re voxels - that's a challenge for another day
I imagine you could use both. Screen-space stuff like this is great for capturing the really fine details (which would require an insane amount of memory in a voxel system), so you could combine this with a voxel method for more coarse-detail / longer-distance rays, and/or image probes for really long-range rays.