Well, that really sucks. Why do they create a game that no system can handle? As for my network, it's just a simple peer to peer setup instead of domain.
I guess the only way to probably do this is to just limit the population when playing on the network. When playing just against the computer... yeah it lags a little bit.
I have not tried just playing against my son on the other computer. So far we've just played as teams against 2 other computer enemies as teams with a 4000 population limit. I'll also give it a try to just play against him and see how that works.