Photoshop :: One Plugin Installs - Another Disappears

I've recently installed CS6 on a new Win 7 64 bit machine.
 
I'm beginning to install various plugins (Topaz, Nik, etc.).
 
I think this is the correct procedure, but let me know if it's wrong:  I open Photoshop, go to Edit, Preferences, Plugins, then check the "additional plug-ins folder" and choose browse.  I navigate to the main folder for the product I'm looking for.  For example, Topaz... I'm using 3 plug-ins:  Detail, Remask, Adjust.  I highlight the folder, click OK, close PS, then reopen it.  I open an image, then go to Filter, and find that all three plug-ins are there.  I open each one, make sure that they are activated with my activation key, then close each application.
 
I then went back to Edit, Preferences, Plugins and browsed for the next plugin folder.  In this specific case, it was Portraiture, by Imagenomic.  I highlight the folder, click OK, close PS, re-open, and when I look for this plugin under Filter, I see it.  But, now, one of the Topaz plug-ins are gone.  It always seems to be the Topaz Adjust.  If I navigate back to it, re-do the plug-in from PS, then the Imagenomic plug-in disappears next time I open PS.
 
In each case, I just highlight the main folder (Topaz, or Imagenomic), not the Topaz Adjust folder (though I did try this, and it made no difference).