Outputing from a PC to a Stereo is not difficult, regardless of which sound card you have. You basically need a cable with an 1/8" plug on one end, and two RCA jacks on the other. Connect this to a LINE input, not phono or mic input. Often, an unused Tape, CD, or Aux input will work.
Notes
1) There are some older amps, and some higher end PA type amps that use 1/4" or even XLR inputs. If this is the case, you need an appropriate cable.
2) If an amp is Mono (one channel), you may need to connect the left and right channels together.