You can't expect a High quality sound from a usual notebook on the market except it's a special notebook that designed with a high quality sound. Many people using an external speaker to get a better sound quality from their notebook. and here's the High Quality Mini external speaker from Asus named Asus Xonar u3.
Asus Xonar X3 is an external speaker with a USB connection which has a small enough size (slightly larger than a USB Flashdik) but it produces excellent sound quality.
it uses existing technology in headphones or rather use the amplifier normally found in an external speaker headphones so that it can produce a clear sound and also supports Dolby technology.
Asus Xonar X3 also provides an application that can be used to set the equalizer where each equalizer option adjustable with running applications such as for games, listen to music or watching a movies.
Unfortunately there is no pricing information and when it is launched. Here's the picture of this Asus Xonar U3.