If your sound card works with alsa
you can add the line
/etc/init.d/alsa-autoconfig
in the boot script /etc/init.d/bootmisc.sh
And alsa ver will be actived at eaxh boot.

Also i suggest to add in the KNOPPIX/usr/local/bin/knx-hdinstall some lines like the folling:

# add alsa activation to bootmisc.sh
# In the boot script /etc/init.d/bootmisc.sh if you add line
# /etc/init.d/alsa-autoconfig
# Alsa server start at boot and it ok for my kde.
# In the KNOPPIX/usr/local/bin/knx-hdinstall of my personalized KNOPPIX I have add some line like:

if checkbootparam alsa >/dev/null 2>&1; then
ALSA_CARD="$(getbootparam 'alsa' 2>/dev/null)"
[ -n "$ALSA_CARD" ] || ALSA_CARD="autodetect"
else
ALSA_CARD="autodetect"
fi

noalsa=""
checkbootparam noalsa && noalsa='#'
checkbootparam noaudio && noalsa='#'
checkbootparam nosound && noalsa='#'
checkbootparam NOALSA && noalsa='#'
checkbootparam NOAUDIO && noalsa='#'
checkbootparam NOSOUND && noalsa='#'

echo "# Boot parameter for knx-hdinstall add">>$TR/etc/init.d/bootmisc.sh
echo "# "$CMDLINE >>$TR/etc/init.d/bootmisc.sh
echo "# KNOPPIX/usr/local/bin/knx-hdinstall add " >>$TR/etc/init.d/bootmisc.sh
echo "# 2 lignes to start sound server alsa" >>$TR/etc/init.d/bootmisc.sh
echo "# uncomment to start alsa at boot" >>$TR/etc/init.d/bootmisc.sh
echo $noalsa"ALSA_CARD="$ALSA_CARD >>$TR/etc/init.d/bootmisc.sh
echo $noalsa"/etc/init.d/alsa-autoconfig" >>$TR/etc/init.d/bootmisc.sh

# So the script knx-hdinstall add /etc/init.d/alsa-autoconfig
# at the boot script /etc/init.d/bootmisc.sh.
# May be a futur version of knx-hdinstall can
# transmit.some parameters to alsa and
# set USE_ALSA="" if alsa are detected unsafe.
# Also this option can be offer like for the CUPS server./