Seems like you're in a bit of a catch-22 situation to me. What sort of audio source will you be recording from? If you're recording from a microphone, a mic-level audio input, like the one on the 650, will be of better use to you. However, if you're recording from stereo equipment, then you will want a line-level signal, like the one on the PowerBook. However, the PowerBook doesn't have as much grunt as the 650.
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