This might not be representative of your actual configuration, but I just wanted to point out that you have a typo in the guest authentication module. It should say uams_guest.so (and not 'unams').
Definitely a few typos above, although they were spotted and corrected shortly after posting. I can't edit the posts to reflect what I tested for some reason.
However it's all good, I found the specific combination that got it working.
Many thanks for all of your efforts to keep Netatalk2.X.X alive!
Old clients like the IIgs only support cleartext and randnum authentication. A2SERVER's scripts set up the randnum password for you.
I knew about "randnum" being required (my client seems to reject uams_clrtxt.so entirely), but the part that appeared to make things work better was the modifications to atalkd.conf, in particular the "-phase 2 -net 1" combination.
Leaving atalkd.conf blank generates a "-net 0-65534" entry soon after the service restart, which seems to cause problems with the client I'm using. Forcing that "-net 1" seems to help things dramatically, as does having a zone specified (without either of these options, it seems to not get a response from the server when attempting to connect to the share. A different error to the "authentication methods" one it gets if randnum isn't the authentication specified).
This could all be coincidence or something unrelated, I'm not sure yet. I've got the weekend set aside for testing on a virtual IIGS setup together with real hardware OS9 and G5 OSX setups simultaneously, and I'll see if I can find the magic combination to make them all share the same storage at the same time.