I believe Music Studio is IAA-compatible, although I’ve never bothered with IAA. I usually sample things and build custom instruments out of them.
Needless to say the instruments that do come with Music Studio (both the ones you have right away and the IAP bundle pack) sound great, reducing the need to use outside sound sources to begin with.
The only thing you may find as a drawback is that the automation is only for the filter, and you have to record it rather than have the ability to edit it. A major future upgrade is still in the works, but I have no idea when it’s to come. However, if you want my advice, just buy Music Studio anyhow. It’s still my fave for quickly jotting down musical ideas and expanding upon them.