Basic setup question

I've been spending several hours now trying to simply allow myself to cue on headphones using mixvibes and the U46mk2...
All that happens at the moment is I get both the speakers and the phones playing at the same time - when I click the phones cue on Cross all it does is make the volume of both speakers and phones louder.
I'm not exactly a sound engineer, and the few threads I found that seemed to be relevant all suggested an aggregate or something like that?
Would really appreciate some help on this, I can't really do anything without it.
Thanks in advance! =D
edit: I just looked at http://www.Apple.com/pro/techniques/aggregateaudio/ and it seems to be what I might be looking for, although I use windows.
Also, my version of Cross LE seems to be a bit lacking in the setup options department...
All that happens at the moment is I get both the speakers and the phones playing at the same time - when I click the phones cue on Cross all it does is make the volume of both speakers and phones louder.
I'm not exactly a sound engineer, and the few threads I found that seemed to be relevant all suggested an aggregate or something like that?
Would really appreciate some help on this, I can't really do anything without it.
Thanks in advance! =D
edit: I just looked at http://www.Apple.com/pro/techniques/aggregateaudio/ and it seems to be what I might be looking for, although I use windows.
Also, my version of Cross LE seems to be a bit lacking in the setup options department...