Unable to use external speakers under Mandriva 2008.1 on Amilo Pi 2530

When I try to play any audio, the sound is produced by my internal laptop speakers, instead of my external speakers. When I go into KMix, I can see that the volume for Headphones (which I'm assuming is the line out of my sound card) is set to full and is not muted. When I use KMix to fiddle with the settings for my internal speakers, this works fine, but the settings for my external speakers have no effect. Under Windows XP, the use of my external speakers is regulated by a Realtek program. I