Assuming by digital you mean digital TV. Unless your digibox has 5.1 outputs, such as sky+ you will not be able to hear the broadcast in true 5.1 surround.
You could connect the stereo outputs to a prologic amp and listen in prologic surround sound. The sound output will be electronically processed to provide a psuedo surround sound, but both rear channels will output the same (mono). This is certainly a lot better than boring old stereo.