If I have registered for QT Pro 5 and have a registration # can I enter those details into the QT registration preference in OS X to use QT Pro 6 in OS X?
No, according to Apple, there's more licensed items (royalty-bearing technologies) in QT 6, and a key for QT 4 or 5 cannot be used with QT 6. You will have to purchase a new key to upgrade to QT 6 PRO
Are you sure? I'd think you could just open up your QT control panel and write down the # and username in the Registration option, and then put it back into QT 6's preference pane. Or is this circumventing something it shoudn't? Or does it even work?
Check this link You'll see all the info. The QTPro key for 4 or 5 can only be used with 4 or 5.... 6 Pro is a separate purchase (since QT6 was released). I guess that QT 6 Pro key will not work on QT 4 or 5, either. Anyway, if you upgrade to QT 6, and need the features of Pro, you get to purchase a new Pro key!