I have the M-Audio MobilePre Breakout Box and when i plug my guitar in, open garageband and test the garageband amp settings there is quite a bit of latency. Ok, i lie, there is absolutely no latency......until i plug in headphones/hi-fi into the lineout on my Mac Mini, THEN the latency begins. There NEVER used to be any latency when i did this... If anyone thinks they can help, has any more questions or has the same problem....please post! You know the drill!