sound out on powerbook g3

[Ian]

Hi. I am very new to YDL 2.2 -- just installed it yesterday. But I have 
a quick "newbie" question:

I've managed to play a test MP3; however, the audio outputs to BOTH the 
internal speakers as well as the speakers plugged in to the mini-plug 
audio out. I would like the internal speakers to turn off as soon as a 
headset or powered speakers are plugged in to the audio out (like OS 9). 
Is this possible??

Thanks for the help.

- Ian