I concur with Guitarhacker on this one. Having done quite a bit of vocal overdubbing in various studios over the years, I can say that you always want at least some of the vocal being tracked coming through in the headphone mix. Normally, that level might be lower relative to either the primary harmonic instrument(s) or lead vocal, if you happen to be recording harmonies. The question you might better be asking is how to adjust the mix for the vocalist for tracking. That's a fairly easy fix, as you simpy change the playback volume of each track to suit the vocalist's desires. It's a fairly simple thing. I hope this helps!

-Mark

Mark
2020 BIAB Audiophile, Mixcraft Pro 9
Band: http://www.midwesternlull.com