"Calm yourselves. These locomotives are wholly imaginary, and not (I hope) serious projects."
However... I have now uncovered a real, serious, hexaplex project, conceived in Belgium. It lives on the Franco-Crosti page, which is here. This hexaplex remained only a project, but its planners were definitely in earnest. You only have to look at the quadruplex they did build...
The drawings below are shown here by courtesy of S. Berliner, III, on whose website they were found, in the Apocrypha section.
See these and other aberrations at: ~Berliner-Ultrasonics
Above: The BigBoy Garrett. 2-8-8-4 + 4-8-8-2 A mere quadruplex, but wait...