Don't know if this will help but here goes anyway..
I have an A4000T and a MDD 1.25ghz Mac and an 800Mhz iMac (all macs running Panther / OS9)
I also have an ADSL modem and a 4 input broadband router.
(1)
I set the router up using Internet Explorer (they all seem to use this) inputting my server details, pasword etc
(2) I set my main MDD Mac to DHCP (iMac also) - that's all
(3)
I rebooted with the iMac connected BUT I made my first internet connection using the MDD Mac, then the iMac.
Both connected to the internet OK.
Note 1. Using a router means that most of your connectivity choices are now left up to the router's software setup. Any mistakes in the router setup fouls all the connected computers up.
Note 2 : I haven't yet set the A4000T up yet as I don't have an ethernet card but if Miami supports DHCP I have no doubts that all I'll have to do is simply plug the miggy in.
Note 3 : Using the above method does work for me and friends who drop in with notebooks need only to change their TCP setting to DHCP, plug in and they can surf alongside my Macs.
Note 4 : *** I have occasionally noticed that getting a connection started "sometimes" needs browser input to 'nudge' it. Occurs infrequently.
Note 5 : silly thought but... doesn't one of the Amiga browsers masquerade as Mozilla ? Might be farfetched but that might fool a router dedicated to Interent Explorer into allowing access to the settings.
I live in Japan and had to stumble through using a Japanese language GUI for the router so it should be easier by far with and English interface.
Hope that some of the above helps you get connected.