Distorted sound from external speakers/headphones.

Hello!

So basically, I can't plug in external speakers or headphones anymore, as the sound will only be heard from the left speaker, with a really heavy amount of distortion that makes it un-hearable. The sounds from the internal speaker, is still OK.

I think the problem was because I plugged in a 30 watts amplifier, through the audio port, which now I know might have screwed the sound card on the logic board.

I tried repairing the disk, disk permissions, resetting the driver using terminal, etc, but nothing worked.

Is there a way to replace the sound card, or plug in another one into the logic board, or use one that can be plugged in the Firewire/ExpressCard port that could solve this problem?

Many thanks in advance.