Equalization

Thats what your problem is. What your FL studio is capable of playing is not waht most other audio systems are capable of. You need to create a clean mix that causes the miniumum amount of overlap in the frequency spectrum, and then normalize everything as best you can to 0db. This song for example has a very prominant lead synth that will clip before any of the other tracks you have get even close to, so when you set up your track gain to clipping level, only the lead synth is fully utilized. Dont get discouraged, mixing is tough and takes lots of experience to master. hope this helps