here is the tip again for reference:
Garageband Hints and Tips: Recording Keyboards to Garageband
One of the normal set-ups in Garageband is a MIDI keyboard hooked up to your mac and this MIDI keyboard triggers the built in instruments.
Works great, and give you all kinds of cool editing choices after you have recorded your music.
Sometimes your controller keyboard has awesome patches in it and you want to record these to Garageband. Not a problem... simply hook up the outputs of your keyboard and input these into your mac and record to a REAL AUDIO track in Garageband.
What I like to do is ARM 2 TRACKS in Garageband and record a MIDI track simultaneously with your audio track!!! This offers up some cool possibilities!! It will allow you to layer up your real track with an instrument tract... or create a cool duplicate track to vary your song structure... etc...etc...
OK! now onto my new garageband hint and tip!
a cool variation of the above trick is to record an instrument track in garageband. Tweek it, correct timing, make it perfect!
Now, use MIDI IO plugin to output MIDI to your external keyboard that has it's own cool internal sounds.
Now set up a garageband track to record your external keyboard! Hit record and GB outputs your perfect MIDI track to your keyboard which then gets recorded back to GB!!
Give it a try!