External speaker configuration

I've got my iBook G4 hooked up to my stereo thru a usb-headphone jack cable so i can listen to music over iTunes. One problem i have is that any noises the computer makes also come thru the speakers, very annoying. I've found the button to leave sound effects to the internal speakers but some websites have little animations and nosies which still come over the stereo.

Anyway i can stop this and just have iTunes thru the external setup?

Not that I have found. I do the same thing with my G4 Tower and have the same issues as you.....