You have just uncovered the one area that the articles don't cover.

Assuming that both the directory server and the file server are running OS X Server. Establish the directory server as an Open Directory Master and set the file server to 'Connected to a directory system' and it should work fine. If it doesn't or you aren't running Server on both then you are into territory a little harder.

I hope to be writing more about these topics soon and extending Kerberos beyond a single server (and debugging connections) is on my list.

Tony