The issue with the Voxel producing scripts is that they do exactly what they are told, they take a volume and make voxels. Meaning, the cubes that represent voxels are stacked to form the surface shape but the are also stacked internally, completely filling the inner volume. It creates a solid stack of blocks, not just a skin that is just a skin of planes. So, you have to remove the interior planes to leave a skin and then weld the coincident verts of that skin.
Unfortunately, this means you have to just find a fast way to manually do the reduction. I 'drag-selected' the surface planes and then hid that plane. Then I'd 'drag-select' another set of planes making another surface and hid those. About 45-minutes later, I had hidden all of the surface planes leaving a ton of internal planes. I selected what remained and deleted them and then unhid the planes I'd hidden. Those unhidden planes were now just a skin suface. I selected all the verts and welded them.
I attached a file. you can see your original and the new one, both with a slice modifier so you can see inside to what I'm talking about. I also found a post by one of our best and highly missed contributors to the forum, Steve Curley. If he didn't know how to do something, then no one did. Here's his post as well.
https://forums.autodesk.com/t5/3ds-max-modeling/remove-redundant-internal-faces/td-p/3996846
Rob Holmes
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3ds Max (2023-2025), V-Ray 6.2, Ryzen 9 3950-X Processor, DDR 4 128MB, Gigabyte Aorus X570 Master motherboard, Sabrent Rocket NVMe 4.0 M.2 drives, NVidia RTX 4090, Space Pilot Pro, Windows 11 Pro x64, Tri-Monitor, Cintiq 13HD, Windows 11 x64
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