Ok so I havent used Stitcher for a little while, upgraded to 5.6 unlimited some months ago.
 
I cant for the life of me find how I enter Panorama Conversion mode so I can load my externally edited cube faces. The funky web based manual is going me flash security grief. So no help there.
 
Please how do I get there?

File - Load Panorama
 
Add any one of the cube faces and the software adds the other 5 for you...  
 
Don't forget there's a copy of the manual in PDF format included in your installation.