No, not unless those instruments are VSTs. Or some sample set whose format you understood.

oh, i imagined that. thanks!

so now i have to figure out how to send my MSP messages to two different Garageband instruments

Not possible as Garageband can't handle multiple MIDI input channels.

Maybe Mainstage (part of Logic Studio)?

You can use Logic Express. Regarding MIDI input it has the same functionality as Logic Studio.

mmm... i'd rather look for some lighter - maybe free - application. any tip?

i dont know of any other application you can open a garageband instrument in... does it have to be a garageband instrument? there is a free sequencer with rewire called reaper, max can send midi to this program and you can use VST plugins and AU plugins in it.

thanks to everyone, these tips have been very helpful. i've been learning a bit of vst and SoundFont audio files. For a beginner as i am, as far as I can see, they both come pros and cons.:

- vst > extra poweful, but sometimes extra instable and memory hungry - SoundFont > a flexible compromise between midi and audiosamples. but rarely believable in a composition.

is that right? ;-) in both cases i'm still looking for some believable and free acustic piano instrument. ahah ^_^

ps reaper was very good.