Garageband+iMic?

[Man Cubus]

I need to lay a second track to an existing AIFF file. I also have it 
converted to an MP3 file.
I need the first track played on Cube Speakers while recording via USB 
iMic from Griffin.
Anybody tried that configuration? I need the sync to be really precise.
I previously experienced delays on iMic's input of magnitude ~0.4s.
I wonder if it's the USB bus hardware delay or my Software without ASIO 
driver capability (I was using ProTools 5 Free on MacOS 9.2.2)?
Or do I NEED to buy another audio input device?