With the current firmware, multiple ether dongles will mirror each other. The multicast will flow to all ether dongles that are connected to your network.
I don't think there is a way to restrict multicast messages to specific Ethernet interfaces in the current version of windows...
With e1.31, the last octet of the ip address matches the DMX universe number that it is listening for. To run multiple EtD for more universes, the ip addresses that EtD #2 is listening for needs to be changed. I might be wrong, but that seems like a fairly easy change, but really - are any of you planning more than 16,000 channels for this year? If so, what software are you planning to use? Unless you go Madrix, I don't think the current software - vixen, lsp or lor, is up to the task...
If you are not planning more than 16k channels this year, then this discussion is purely academic.
Regardless, With a little patience, I think RJ will release the firmware you seek. If not, you can still use your USB dongles for additional universes.
RM