Having trouble cueing up track in headphones!

Hey out there.... I'm new to djing, I've been doing it for about 2 months now and I'm definitely loving it. But I decided to go out and purchase a numark dj io... Well now I am having trouble cueing up the next song into my headphones. I am using a numark mixtrack and running virtual dj le. I did not have this problem when I was splitting the headphone jack in 2. Can anyone help me out thanks!

Can you specify your problem a bit more?

you need to make the main out in your software channel a (or 1+2) and the monitor out channel b (or 3+4)

I'm not able to hear the next song in the right side of my headphones... it just plays in the headphones like a speaker