Comment Re:It's like telling a Photoshop user: Try Paint! (Score 5, Informative) 299
Garageband is (at least up to 2010ish - not sure if recent? versions have robbed anything) a surprisingly powerful music program. Logic (& other daws) add a lot of editing specific features that really enable you to get extremely anal with your work, but all of the underlying 'record/punch/trim/level/etcetc' concepts are there and do what you expect them to do. Garageband does notation along with midi / wave substitution and add in the JamPacks (all included free with MainStage on app store iirc) to replace stock GM sounds and everything the topic poster wants is there.
A better analogy would be telling a Photoshop user to try GetPaint.net / Paint.NET. Not the same as Photoshop, but all of the essentials and editing concepts are nearly identical. You can easily accomplish whatever it is your trying to do.
$.02 As much as I love and try to solely OSS, there are no options for this specific case. Ardour and Rosegarden are nice enough, but in much the same way Gimp isn't Photoshop, neither are those suitable alternatives. (primarily, asio-ish low latency audio/hardware isn't reliable ime, and there are no real options for upgraded GM soundbanks short of creating them yourself (which will end up consuming easily 88x more time and energy than the music being written in the first place))