f you purchase Mainstage 2 from the Mac App Store you can download all the Jam Packs (loops & instruments) via that app for free. You can then use all the instruments included in the Jam Packs in Mainstage and Logic Express or Logic Pro. Basically, if you already own a version of Logic Express (I own Logic Express then you get access to a huge raft of new instruments, including the EVP88 electric piano simulator, EVB3 organ simulator and the loops within Logic Express. The Sculpture plugin appears to be barred from Logic Express.
In GarageBand, you can use the added amps and stomp boxes that Jam Pack 1 included. I cannot seem to access all the loops from GarageBand but this appears to be a bug I am experiencing. I could not see them all in Logic Express either until I re-indexed my loops. That doesn't seem to have helped GarageBand's Loop Browser for some reason but that appears to be a separate matter.
then you get access to a huge raft of new instruments, including the EVP88 electric piano simulator, EVB3 organ simulator and the loops within Logic Express. The Sculpture plugin appears to be barred from Logic Express.