(Audio noob)
..if I don't have a DVD player and only have an S/PDIF connection as an Audio-out.
EDIT : Also, ofcourse, speakers in question don't have SPDIF input
There should be an analog headphone/line-out 3.5mm jack or RCA out on your TV which can go to your 5.1. Of course it will be stereo only. Most 5.1 sets will be able to simply expand the stereo signal across all speakers.