I'm on GarageBand 11, I contacted Apple and they just gave me my money back, which obvioiusly didn't solve the problem. Everything downloaded fine
The new instruments will only show in GarageBand 10.0, not '11. Don't you see them in GarageBand 10.0? You can keep both versions installed. They do not interfere. And the applications do not need much space, only the installed instruments and loops.
Oh and if this doesn't end up working out, is Mainstage 3 a good substitute for GB or is it more of a tool to complement GB
MainStage is a tool for performing music, not for mixing song files. But installing MainStage will give you the JamPack instruments and loops to be used with Garageband.