SP/DIF problems

I had a problem at my last gig. I could not get sound from my stereo reciever when I conected my laptop via the shared Headphone/SP/DIF port. The laptop is a Toshiba Satelite M305D-S4830 running Windows Vista premium 64bit. The audio device is Conexant High Definition SmartAudio221. I enabled the device in "Sound" and also enabled all submenu options that I thought were appropriate such as supported formats DTS and Dolby Digital and enabled Vitural surround which encodes the sound. I also tried with thease options disabled. I ran a 1/8inch mono minijack from the shared headphone-SP/DIF port on the computer to the RCA coax digital input on the reciever. I have used that input to conect DVD and cable boxes to the reciever and got sound. In the amp menu I enabled Auto detect and the reciever suports DTS and Dolby Digital. I did get sound when I went back to analog input using a stero 1/8 minijack to L&R analog inputs on the reciever and enabled "Speakers" in Sound. Any sug.