help with using other external sound I/O

Hi all. I just stumbled upon this forum and had to join as in the two days of lurking it's already been very helpful.

I'm going to try my hand with a DJ control surface. I'm not new to computer music, I've got a fairly elaborate set up already with many synths and control surfaces. But that's my problem, all the reading i've been doing seems to assume the usual set up is laptop, dj control surface and audio2. I've not managed to find any information on using other external soundcards that aren't exactly designed for DJing.

So my question. I have all my monitors set up (2 for mids, 2 for highs, and 2 for lows.) My I/O (what seems to be called an external soundcard in DJ lingo) is an ionix which only has 1 set of outputs that is then split by frequency through a rack unit to each of the sets of monitors. So with all of this I really don't want to have another external sound card just for the cue mix in my headphones.

I'd love to get a vci100, all my research has led me to think it's the one for me. Is it possible to use the standard headphone jack on my macbook pro for the cue mix? as in does traktor or other DJ software see the standard audio out of the MBP as a "soundcard" so I could run the main through my ionix like usual and use the headphone jack as the cue mix?

Thank you in advance for the help. and thanks for these forums, they've already been great to read and I'm sure I'll be using them constantly in this new venture.