I have the Kameleon KD-LX100 and am using an external input. The HU should be pretty similar so here is what I had to do to get mine to work. I believe that the HU is set by default to accept a CD-Changer input so you will first have to go into the setup and change it to Line Input. This is how I did it on mine if I recall correctly.
1. Hold the "Sel" button until it takes you to the setup screen. (This is where you can set the Clock, Bass, Treble, and Fader... etc...)
2. Scroll with the Up and Down Buttons (Track Forward, Track Reverse) until you see something like "EXT INPUT" or something like that.
3. Turn the volume knob until the option shows "LINE INPUT" ... on mine, I can choose between "CD CHANGER" and "LINE INPUT"
4. Hit the "Sel" button again to save settings.
5. Now When I want to use the external input from my computer, I just hit the Blue Source button and that allows me to switch between FM, CD, and the external link.
How this helps, let me know how it works out.