Connect your 5.1 amplifier to your PC and your speakers to the amplifier. The sub can sit anywhere in the room without affecting its performance, since the human ear has difficulty in determining the directionality. The remaining speakers should be set up in the standard 5.1 layout (See References). Imagine a circle around your chair. Place one speaker on the circumference, directly in front of you, then the other four on the NW, NE, SW and SE points of the compass.
Measure the distance from each speaker to your chair, they should be as close to equidistant as possible. If the shape of your room makes this impractical, try to balance the individual volume controls on the rear of each speaker so that they sound level. If you play a piece of music through all speakers at once and sit in your chair, none should sound any louder or quieter than the others.
Locate the output channel on your mixer. Insert the surround plug-in into an effects slot. Double-click the plug-in title in the channel strip and the edit window appears. The majority of surround mixing software uses a similar interface. An overhead "plan" view of your mixing area, a square or circular space. Each of the five speakers will be represented by a numbered icon, and each of the tracks in your multitrack project will be represented by a small dot or marker, floating within the space.
Adjust the "Pan" control on each channel of your mixer. It doesn't matter what you set each value, just that they are all different. You will notice that within the surround mixer plug-in, the channels appear fanned-out along the center-line of the space, rather than piled on top of one another in the middle of the space. Click each marker representing a track and move it within the space, you will be able to hear the sound moving between the speakers that surround you. Continue until you are happy with the locations of each sound.