Searching for installed kernel modules using locate I found the actual
modules for the DAC are installed. However, using modprobe did not
result in the modules being loaded. Modprobe complained with the
error:

modprobe: FATAL: module name not found in directory /lib/modules/4.16.12-v8+

After that I used depmod to create the necessary module dependencies,
but failed again to successfully load the modules.

To arrive at the this point I consulted the IQaudIO manual for the DACs.