Total posts : 45366
Using version 1.6.1 I am able to open two instances and load different play lists to each. I cannot try multiple sound cards to check if that works.
Are you able to start multiple instances without playing? If not, maybe it has something to do with the version you use or maybe with the configuration files.
Check back since there are some real experts on Zara use here who can probably give you a better answer.