Hi Per,
Only incomplete trials/demos of the old versions remain, and there is no way to activate them.
There were plans to make the full legacy versions available for free, but they have not come to fruition yet.
As someone who bought a license to the blue FxSound Enhancer back in the day, my experience has been that the sound boosts achieved with the Equalizer and the Effects of the blue version, were pretty much identical to the current purple version.
The main differences are improvements made to the Equalizer sliders, and to the Visualizer.
Also, the latest update to the purple FxSound now supports up to 100 additional Presets.
Actually, come to think about it, there are many more improvements: adjustable frequencies, customizable shortcuts, minimalistic interface, multiple languages…