So I've been reading through the ACT documentation but can't figure something out.  I only want my MIDI keyboard controllers to effect softsynths.  How can I achieve this?  Right now it seems to effect whatever the active window is.

I really want the controllers to do NOTHING unless a softsynth is open.
 
Any help is appreciated!

ACT dynamic mapping (with any CS plug-ins) always control whatever VST plug-in is in focus. It can not distinguish between strip FX and Synth. Once some plug-in got ACT dynamic map focus, you can "ACT Lock" it so ACT no longer follow mouse focus. That locking is session specific, it is not saved within the project.
 
Also note that the focus is for plug-in, it is changed not only when you open its GUI but also on clicking corresponding line in the FX bin or Synth rack. CS can not detect either GUI is opened.
 
It is possible to configure my CS plug-in to control specific parameters of specific synth, independent from ACT dynamic mapping and so from the focus, can be parameters from different synth. And it is possible to set some conditions when that happens (for example, during play or record). But general limitations still apply, some informations/conditions are simply not available for CS plug-ins.