Funny you mention kd's, chi o's and zta's, b/c those are the only three sororities we have on campus here
We had a dinner exchange and all-sorority social. What we did was all the groups passed around a sheet and you would volunteer to either go to another house or stay at your own house (the latter in order to make sure there would be girls around the house too). That was for dinner. We specified nice dressing (not quite pin attire but not really jeans tshirt either) and had nice food out, then talked during dinner and played games and watched movies. So there were girls from all three sororities at each of the houses and I think it turned out to be pretty fun!
~april