I don't mean to sound as if I am passing you off, but have you tried
Emachines Support? Looks like E-mail support is free. If you have a service plan through your place of purchase, give them a call too. Beeboy is absolutely right, as long as you use the onboard sound, you will be running on luck. there are several good cards to choose from, my current favorite is a Turtle Beach Santa Cruz, with the old standby being a soundblaster live! 5.1, which you can find in several places for around $30 US.