There was an extra cost "add-on" to 5.6 that let you stitch 2 greater than 180° FOV fisheyes the way iPIX does.
Double Stitch was introduced to switch VR photographers from iPIX to SU when iPIX Corp went into bankruptcy
When Autodesk bought Realviz and streamlined the product line, Double Stitch was inlcuded with SU at no extra cost
If you're not working with the Nikon FC-E8 or E9 Fisheye Convertors for the Coolpix cameras, you probably don't need DS
Doug Aurand
Albuquerque, NM