the reason your line in doesnt work on the new ibooks is interesting. my friend bought the monster cable (1/4 in - 1/8 in) off of the apple website and it works fine if he plugs straight in.but on mine i have to use some sort of buffer(a mixing board) to get enough volume out of it.so it may have to do with the settings on the new audio in ports. they may be set to a lower input level. im not sure
Recording on the Cheap