Legacy formats and software is always a crapshoot, I've found a few leads that might help you.

From an article back in the 2000s "A plug-in for 3D-Studio MAX that allows importing and exporting SPX data into and out of 3D Studio" Maybe try and hunting that down?


[This legacy software might work for you][1]

[Or some of these might.][2]

It looks the the German company that originally developed it changed from Interzart to Scanbull Software around 2006 but I can't seem to find any other information about them.

Their software was 3D Editor Marlin, so unless you get extremely lucky on ebay you might be out of luck.

[This git repository of old software][3] has several versions of Dimension 3D-Systems GmbH - Open SPX Plugin which might help.

This was all the information I could find with limited research time, hope it helps!

  [1]: http://www.parallelgraphics.com/products/vrmlpad/download/
  [2]: https://www.web3d.org/x3d/vrml/tools/authoring/
  [3]: https://gist.github.com/afiestas/135cc16b2ec7a6cca4a7185b3bb38e2d