You will need to backup:
The Mainstage Application
Library:Application Support:GarageBand:Instrument Library
That should do it?
It might be easier to download the Additional Content installers directly (rather than using the in-application method), so that you can backup the installers themselves.
From another thread on the forum
Beautiful! Thanks very much. I will DL the packages.
I do have a curiousity question though... I have ALL the Jam Packs (including the discontinued JP1), and I installed them a couple years ago, without issue. They all seem to work perfectly with GB9 (v6.0.4). So, I am wondering, why Mainstage needs to re-download all this content? Is there additional content that is not on JP DVDs?
Possibly because the loops on your Mac are not in the standard (Factory) location?... most of mine are on a different drive, which both Logic & Mainstage do not seem to 'know about'.
There does not seem to be any difference regarding the overall content of the downloads (loops/instruments etc) except that the loops are now supplied lossy/lossless compressed. As best I remember, the JamPack DVD's come with full quality (and 10x larger) aiffs???
I don't thing the location is an issue as I installed with the defaults, and Mainstage finds them OK.
When I use the Download Additonal Content, MS2 shows the Jam Packs Status as incomplete, showing the Apple Loops are installed, but the Instruments are not. I checked and GB finds all the instruments, and when I check :Library:Application Support/Garageband on my G5 Quad and my MBP, info shows the same folder size and number of files.
Even the :/Library/Application Support/Logic folders are the same size. As well the Date Modified dates all match up.
Unless there is anothe folder where the content is being saved to, I am at a lost as to why MS can't find the content, or where the new content is being installed.