As I mentioned previously, other options are sound-card or/and speaker upgrade.
Unfortunately your system is old, those speakers are tire and probably wont go down below 75 Hz wth the power is probably 80W and the amp is no less than .7 THD. Your system may not even have SPDIF connection. look behind your system and if you can't find digital connection input then it has no SPDIF connection.
So your first choice is to download the software mention above leave it to default, play music and increase your system volume. If the sound is distorted then you're system is probably can not handle frequency below 50Hz. Then the question is, how much are you willing to spend for a better sound? A sound card would enhance your sound but your speaker capability is limited.