Buying an external sound card and a decent sound set or headphones usually do the trick. In general you don't mess with the sound and you never equalise sound, that makes it sound terrible.
In general treble is the cleanliness of the sound, but too much treble makes your audio sounds shallow and sharp. Bass adds warmth and depth, but too much bass and your audio gets overshadowed and lacks detail. Best not to mess with it though unless you know what you are doing.
Please excuse my (probally) poor grammar







