M-Audio Delta 1010 Sound Card "krk monitor" Questions

...between a "Sony VAIO FW-21M" laptop (with Windows Vista 32 bit OS) and a pair of powered monitors "KRK RP6". I installed the driver and the audio device works fine if the laptop is on battery mode, ...

...to get sound from the S/PDIF output on the card. I ran RCA cables from there to the inputs on my KRK ROKIT monitors and all I can hear is a VERY faint crackle of the audio I'm playing. I can use ...