there is software 3D environment codecs that you can turn on and off. if your application has 3D audio support or surround sound, yes you will get the feeling that the speakers go in and out to give you the surround feel. if it is off, then your two speakers should be fully on.
i would just test it by playing music and put the fade left and right to see if they both come on. the fade front and back should be disabled by default.