I think what you're doing is confusing the UVs the -uv2 is just for the AO map. it shouldn't have any texture data.
try exporting the katana twice, once as "katana.obj" and the 2nd time as "katana-uv2.obj" without making any changes to the model between exports. then import it into s3d and click the load .obj files and you should see both pop up.
I'm going off of memory so I may be mistaken, but this is how I remember doing it
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