Thanks for the insights - indeed I were able to buy the commercial Envoy 3 (from the usual auctions) which got an "inofficial" update from Heinz (privately) some time around the launch of the Sam440EP (to make it OS4.1x compatible). Of course I had to configure Envoy with the mentioned 2049/2055 packet types for running with TCP/IP in parallel...
Since then all my "AmigaOS" systems (AmigaOS 4.x, 3.x and MorphOS) happily have both "stacks" running in parallel with Envoy as my main data exchange stack between the Amigaoid systems.