Reply to Cueing without soundcard?

Just a quick question, after reading some stuff I came to conclusion that I need to buy a soundcard for cueing, right? I am using terminal mix 4 and I can't set up headphones to work properly using controller, the options I got in output routing is terminal mix 4 1, 2 ,3 and 4, I dont know what 3 and 4 stands for. Thanks.