Pursuant to picture above that SOUNDCARD 1 to speaker, and soundcard 2 to headphone as if to preview mix in headphone. If soundcard 1 set as master output, so that soundcard 2 is headphone. when you mixing in virtual dj activating CUE MIX of function. This setting using 2 soundcard with same of brand for djing using virtual dj software. tutorial here. you can using onboard sound in your computer too but if there ae the trouble don't use it. why use 2 soundcard with same of brand?? using soundcard same can make output of result do same. you only setting in sound control in control panel, then cek out volume each it. how to set config in virtual dj here.