I just picked up the Logitech z-640 speakers and set them up, but the rear speakers aren't working. I've set the speaker setup in windows to 5.1 sound and checked the box for rear speakers to the line in and the center speaker to the mic, but still nothing. Is there anything else you have to do to make the line in and mic jacks work for the rear and center speakers, or is there anything else I could be doing wrong? Thanks