I'm fairly certain that when I saw both connections being used (in through ethernet and out through firewire) I had gone to a folder via Windows' 'my network places'.  If I go in through the Workgroup panel only the firewire is used for both in and out... so the solution is to just make a desktop shortcut to Z2 in the workgroup panel.  I had considered messing with the windows hosts file to make 192.168.1.100 point to 6.6.6.2 but I don't think it's necessary.  So I guess that means that if I (or any application) were to go to Z2 via //Ziggo2/ShareName it would use both connections, one for incoming and the other for outgoing.  I'm copying 12+GB of jpeg, tiff and psd files over firewire now and have no activity on the ethernet - exactly what I expected to see.