Vocals are very weak on mp3 files after instaling new sound blaster?

Hello, I bought a new sound blaster by Creative, installed it, everything works great, except when I wanna listen to music. all the track is great, but the singer's voice is very weak, can barely here it...where is the option that will fix it? i got windows XP, the sound blaster is 5.1, my speakers are 2.1...thanx