I have a soundblaster x-fi sound card and a Klipsch Pro Media speakers hooked up to the sound card and it works great. I have my machine hooked to a 32" Samsung HDTV and am trying to find a way to have sound come from the TV also. I tried hooking the tv to the gigabyte on board audio out but I still get no sound.
If you have a sound card, onboard sound should not/will not output.
You would have to figure out a way to run sound from the sound card/speaker system to the TV. You could try splicing wires, but that seems a little sketchy to me. Do you have multiple outputs on the sound card?
I think it's likely that you're going to have trouble running output to more than one device at once. You could probably set something up where you can flip back & forth, but generally TV speakers are meant as standalone devices, to be ignored when you get something separate/better quality.