The system works quite well now. Here's an example of formatting a disk in drive 2:
Using the COPYM2 command the system disk can be copied to this new disk. The new disk is then bootable as well.
Recently I've added the centronics port. To test it, start MAME like this:
mame psi98 -flop1 kos605d -flop2 util605d -prin output.txt
After booting the OS, enter the following commands:
(loads the generic parallel output driver)
(print the file KOS.INF to this driver)
output.txt now contains the KOS.INF file.
I'll probably mark the system working soon, unless I find major issues.