If you notice cross-talk (cue channel in the main channel and vice versa) you may need to optimize the Air and Cue cross-talk.
Click the icon in the toolbar.
Click on the Cal button for the "ON AIR" output device.
In the Optimize Air & Cue Cross-talk section you will need to adjust the Optimize Air & Cue Cross-talk sliders to suit your system.
The idea is to get a clean stereo cue signal that does not "leak" into the air channels, and vice versa. The test tone function plays a simple waveform through the left channel of the cue only. The goal it to isolate this tone so that it can not be heard at all through the air channels, and only very slightly or not at all through the right cue channel. Also pay attention that the overall volume level is close to, but not louder, than when you use the same soundcard in normal stereo mode (no cue), otherwise distortion may be occurring.
Tip: Be sure that the soundcard you are using is set to use all 4 speakers. The method for doing this varies with soundcards, though Control Panel -> Multimedia Properties is a good place to start.
Note: Some 3D soundcards have poor driver calibration or do not perform hardware mixing of 3D buffers meaning you will not achieve the ideal no matter how you place these sliders. Obtain a better soundcard driver or soundcard.
How to configure a four channel soundcard for cue
Cue channel output options
How to set up your soundcard (main channel)
How to calibrate your soundcard