From my experience, the Apple Ethernet NB card will work with any standard MAU. I don't ever remember needing special MAUs. Then again, I was running System 7, and perhaps the A/ROSE extension was newer and provided some changes.

If I remember correctly, you can set the port speed and duplex on the Airport. Can you try setting to to 10base-T at half duplex, then connecting directly to the Airport and see what happens?

Another thing to test is to statically assign your TCP/IP information and use a Unix machine to run tcpdump to see if there's any traffic coming from the Iici.