I'l take a stab since nobody has replyed to this post.
Alright try this, just before you mix everything down or turn it to wav. Make sure nothing clips. I have never used FL-Studio but I am sre there is a way to check the levels. You may have to turn down the volume a lot. I know acid has a monitor on it. You want the sound levels to almost clip but not quite. Like if there are colors, green, yellow, and red. Red is cliping, you want it somewhere just barly licking the yellow. Again when you mix it down it may sound really low, still do it anyways. Once you have your wav, bring it into a program like SoundForge or Sound Edit. Use this program to boost the levels. Since you made sure nothing cliped, when you boost the levels it should be like you are just turning up the volume.
Now Master is not my best subject. Though I hoped this helped, or made some sense, and maybe somebody that knows a lot about this subject will reply to your post.