What's the model# of your Klipsch sub? I had a feeling your sub was active, bc you mentioned a line-in connection. Your sub is active if it plugs into the wall? You're good; this should be very easy.
To get the signal from your PC in order to amplify is simple - you have a headphone jack. You'll need a compatible STEREO plug with cable, a "Y" adapter, so you can split the signal from the jack on your Dell, between your sub and the RCA connectors on your powered Edifiers. Use the gain and crossover on the sub to tailor the sound to suit you. If the sub has a phase switch, versus continuously variable (0-180 knob), experiment with room position, phasing and also rotating the sub 90 degrees either way. You want the sound waves from your sat's (Edifiers) and the sub to be 'in-phase' as close as possible. Bass can suffer if they aren't. Think of it this way: you want the cones all moving in a direction which will reinforce the sound waves. An out-of-phase scenario will CANCEL certain bass frequencies. Good luck! You have a nice rig and it should sound great.