I have test knx-hdinstall wth the folling uncommented line instead of the line of my late post
on alsa after knx-hdinstall.:

noalsa=""
checkbootparam noalsa && noalsa='# '
checkbootparam noaudio && noalsa='# '
checkbootparam nosound && noalsa='# '

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 $noalsa"aumix -w 60 -v 60" >>$TR/etc/init.d/bootmisc.sh

# use Knoppix-generated modutils/1alsa and alsa-0.9-knoppix
cp -af /etc/modutils/1alsa $TR/etc/modutils/1alsa
cp -af /etc/modutils/alsa-0.9-knoppix $TR/etc/modutils/alsa-0.9-knoppix

I was inspired of the folling lignes in knx-hdinstal:

# use Knoppix-generated XF86Config
cp -af /etc/X11/XF86Config $TR/etc/X11/XF86Config
cp -af /etc/X11/XF86Config-4 $TR/etc/X11/XF86Config-4

1alsa and alsa-0.9-knoppix are copied in /etc/modutils/ of the target partition

and "aumix -w 60 -v 60" ais added to bootmis.sh

But sound card not work on reboot on target partition!