You need a 5.1 sound card, preferably with an optical output for future speaker system upgrades. However, the sound system you have does not facilitate optical out... Depending on your motherboard, you might already have a 5.1 sound card onboard. What motherboard do you have? If you absolutely must have a dedicated sound card, I don't see how you will be able to get anything better than the Asus Xonar DS for $35. It is a 7.1 sound card @ 24bit with max of 192 Khz sample rate and 107 dB Signal-To-Noise Ratio.