I’ve been looking for a way to improve the sound quality of iTunes (for Windows) for two years, but up until now was unable to find a good solution. But I came across SRS Audio Soundbox and it works very well.
Unlike some of the other DSP (Digital Signal Processing) add-ons I’ve tried, SRS works at the system level instead of application level so it improves the sound quality of any audio coming through your soundcard. It includes profiles based on audio content type such as music, movies, games and voice.
The improvement is substantial and makes iTunes fed mp3s sounds a lot better. It’s well worth the $20 to register, but you can try it free for 14 days.