Hi Isabell,
With Media 100 i v8.3.2a, if you want “good” clips in your bins AND you want to playback video, you MUST stay at QT v7.5.
If you don’t care about the clips in bins being purple (some say it’s pink), then you can go to v7.6, but I don’t recommend it ’cause there’s really no pay-off and we have no idea what will happen with v7.6.1-7.6.4.
I expect your next question will be how to back up iTunes, and I don’t know the answer to that one, sorry. Though I imagine it would be done much like you would back up QuickTime.
Hope I caught you before you made your day too much more difficult.
~Wick