Control sounds volume

hi,im trying to make a music/sound control and FX sounds control,so i have my FX volume level as a variable(FX_vol) and also the Music/sound volume level as a diffrent variable(M_vol),so i set them as sounds that i can use trough coding:

S1 = new Sound();
S1.attachSound(“soundFX”);

S2 = new Sound();
S2.attachSound(“soundM”);

and let the normal sound loop:

this.S2.start(0,99);

and i set that the sounds are allways getting their volume level(replace the old volume with the new one - for the player to set the music volume level and the sound FX volume level)
so it looks like this:

function onEnterFrame()
{
S2.setVolume(M_vol);
}

and on that function i added an option of when the FX sound will play(when the player hits the ‘Z’ key)
and it looks like this:

function onEnterFrame()
{
S2.setVolume(FX_vol);
S1.setVolume(M_vol);

if(Key.isDown(90))
{
this.SW.start();
}
}

*dont worry i added something to the code that you have to realease the Z key to press it again and make the sound again(so the problem is not here)

and when i run it both of the sounds(music and Fx) stays on the same volume and when i try to change the music volume level (in the running-i have some kind of a volume slider) and when i try to change the sound fx volume level they both stays the same,and dont change(not the sound fx and not the music…)

how can i fix that?