I don't think SiteImport 3 works on CS6 Mac... we did quite a few updates for CS6 on MAC in Design Extender... I think you may need to upgrade to get it working on CS6 or use CS5.
I went ahead and gave you an additional $200 off your upgrade to Design Extender so that you can get it for only $99. The discount is assigned to your account, so it will show in the shopping cart when you are logged in.