I knew it was possible, but up until now I had not taken the time to figure out exactly how, to combine a lightmap with tiling and modular textures. Now I took out the time to test it and I made a small video tutorial. Why not share it with all of you?
Sketchfab can handle lightbakes very similar to how a game engine would handle lightmaps, and you can archive the same results. But you have to bake and set them up manually.
This is by no means a discredit to the Sketchfab exporter for max. It works great. But I found the way it works with baked lightmaps in combination with modular textures not ideal and also not representative with how a game engine would handle lightbakes.
Have a nice day!