I noticed that GarageBand appears to have lost the ability to import other instruments or libraries. Is there a way to import third party instruments into GarageBand in 10.3? Along those lines, where are some good options for additional instrument voices for GarageBand? Apple used to have the option to purchase sound/instrument libraries, but no more.
If you previously purchased GarageBand 6, it will be available for download in the App Store; the two versions can both live on the same machine just fine.