Title explains itself!!!! I have a sample, ok i first layout the melody and stuff that i want, but in the song that i am sampling there is a voice that i want to layer over the melody that i did!!!! For some reason when i try to layer it, it like stop the original melody that i have playing!!!

I hope you guys understand that, and thanks for the help

Use the combinator. You can put as many devices as you want into a combinator and sum them together in a mixer (which is put into the combinator too). Then all notes are played with all your devices simultaneously.