MiamiDX is not Freeware, it is only the Demo on Aminet. You should be able to connect to the internet through ADSL with the Demo Version of MiamiDX. The PPoE device should work, but you will be disconnected after 30 Minutes.
one way around the disconnection is to set up a arexx script that disconnects and re-connects miami every 20 mins or so. This resets the timer of the cut-out and the dis and re-connection is quick enough that it shouldn't bother you.
What about when using provider with dynamic IP? Even most DSL providers do that. Reconnecting changes the IP in most cases, so it would break sustained connections like IRC, streaming radio, so on...