hi, i have an electric guitar and this is what i want to do. Connect my guitar to my mac and through garageband add effects and the sound to come out of my amplifier. my problem is: i have connected my guitar to the imac line in with an adapter and my amplifier to my line out (headphone input) with an adapter also. i can now here my music or videos my mac plays through the amplifier and i can RECORD my guitar in garageband and AFTERWARDS here it through my amplifier but NOT WHILE PLAYING. any help? thanku