when i was using 3dgs multiplayer i had 4 players and 60npcs running smooth with a dsl as host. i wouldnt say its impossible to make an mmorpg type game with a6 but unless youre some godlike coder it wont be possible and secure.
i released the code from my previous multiplayerproject right now, its commented pretty good you can find it at my homepage http://www.ackbytes.de under download.