Preview music while playing

I am trying to find a way to be able to preview music in headphones while playing out to speakers (think DJ). I'm looking for a way to do it with dual sound cards but using iTunes for the playing the live sound. Is there a way to do this without resorting to specialized hardware and software? If not, what's a good low-cost solution? The primary goal is just to be able to preview songs with headphones to add them to a live playlist. Any help would be appreciated.

 

A simple solution would be to use the on board sound (make sure it is enabled) then buy or use another Sound Card to play out to your speakers (make sure it is enabled). You could use iTunes (hope I got this right) to default to the Sound card and use another app (Real Player, Windows Media Player, or VLC Video LAN Player) to play the sound into your head phones (on board sound device). Speaking the obvious, make sure you have the headphones plugged into the on board jacks and your speakers plugged into the Sound Card.

Otherwise, you are going to need a sound card (or media center - hardware) and software that can multi process sound output to different external devices. This can get pretty expensive.