In fact there were two problems. The quirky one was about a pin on the hardware interface, related to speakers, not being activated.The problem is solved with help of ChatGPT, and, to be honest, I don't really understand how and why it works,because it is very much hardware related. The sound device I am using is:

Audio device: Advanced Micro Devices, Inc. [AMD] FCH Azalia Controller (rev 01)

It is Realtek chip, far as I can understand. Rather common sound hardware. It works fine with Slackware on the other partition. The solution which worked was to add the following to /etc/rc.local I have modified the script a bit

(
SDEV="/dev/snd/hwC0D0"
sleep 5 
if [ -e $SDEV ]
then
   hda-verb $SDEV 0x15 SET_PIN_WIDGET_CONTROL 0x40
else
   echo "$DEV not found"
fi 
alsactl restore
) & 

'hda-verb' line is the key. I wish I understand the problem better, but I don't. I hope it might help somebody else with similar issue. Also, I should say that Excalibur was installed from single 'server' CD image (around 650M).Perhaps the installation from some larger image solves the problem somehow.

The second problem is trivial compared to the first one. I have two sound device on the system. The other is HDMI device in the NVIDIA card. It works with speakers attached to the monitor, which I don't have.  So I blacklisted the device :

blacklist snd_hda_codec_hdmi

Also the initrd needs to be updated with update-initramfs. This second issue might be trivial, but till someone might lose hours getting around it.

Either way, the sound works now.