Improving Sound quality

[pollitix]

G'day from New Zealand - VLC is a life saver! My only problem is that I download an increasing quantity of stuff that is described as having AC3 files etc. When I play stuff on VLC the sound is often a bit muffled and indistinct. I have tried selecting different audio options but none to seem produce high quality sound. I am using a jack from the computer to left and right audio jacks on my amp. Any help would be greatly appreciated. Thanks