I found a simpler way to change the sound output device than using PulseAudio.
Code:
cat /proc/asound/cards
shows the sound cards installed in the system. In my case the sound card I want to use has the number 1. I create a configuration file /home/knoppix/.asoundrc with the two lines
Code:
defaults.ctl.card 1
defaults.pcm.card 1
I can adjust the volume with the program alsamixer (or aumix). After restarting the Xserver the volume control in the LXPanel works with the new sound card. If the the web browser is running using the flash plugin while I change the settings for the default sound card then I have to restart the web browser in order that the flash plugin uses the new sound card for playback.