What I am looking for is a extension cable or something to move the whole subwoofer further away from the Tower.... Is there such a extension? or maybe I have to get a extension for each individual audio cord coming from the Tower?
all logitech 5.1 systems hook up in the same way generally 3x 3.5mm cables which go from pc->subwoofer using 3.5mm cables then the individual rca plug end cables which go to the speakers with one of them (front right normally) being a special pin arrangement with control knob on it. some models however did not have this special pin.
removed image since you clarified model]
three 3.5mm extension cables would give you more room to move the subwoofer away from the tower by extending the reach of the three cable inputs however you will still need to keep it nearby (perhaps the other side of the desk) since on models with the special pin for front right speaker you would be limited.
removed mention of Dsub plug since the x540 doesnt have that like the other sets do.
given that logitech uses the subwoofer as a hub and has the speaker amplifier inside.. unfortunately that means needing to extend quite a bit of cabling if you want things moved more than the original cables allow. as long as your extensions arent too much longer i think you should be fine.