I was recording some guitars, bass guitar and regular electric guitar, by plugging through the headphone-out on the amps and straight into the line-in port on the MacBook. The guitar was absolutely fine but the bass guitar seemed to cause some damage. The apple genius said it was the logic board that was broken? anyway, how can i stop this from happening again. If i was to guess, i would say that the signal from the headphone out (on the amp) was "unbalanced" and so that somehow blew the line-in port. Would this, http://www.dolphinmusic.co.uk/product/8531-behringer-ultra-di-di400p.html , stop it from happening again as it outputs a balanced signal. if not what would help. I'm on a very slim budget.