Better update here as well.

The "Bad Adress" error shown above is to be ignored. I've got everything set up and working now. Using OpenTransport, automatic DHCP lease and even automounting an AppleShare from my Raspberry running netatalk. 

Using the 7.7.2 driver with System 7.5.5.

Running the diagnostics in this working state still throws the same error in my face, but obviously everything is running fine.