Thing is, when I want to add vocals to my beat, what I do is:
1- I make my beat and i track it (make a different sound file for every instrument in my beat (kick, snare, drum, bass, hihat, clap, piano, etc...)
2- Dump those in another program to make the recording (like Adobe Audition, or Pro Tools)
3- Since all the instruments are seperated, you can adjust the volume of every instruments seperatly.
Now, if you want to have a intrumental of your beat, well, in that case, you dont need to take the vocals into account, IMO... if you want people to just listen to the beat... If I sell a beat, I always sell it as a whole in a file (for listening) and tracked (for recording) ...all in one CD... that is, if I SELL the beat, not when I lease it...