On the VS1680, you can insert (yes instert) the reverb on the destination track and send it to the aux (pst) for some headphone amp. Edit the reverb settings to set the direct level to 100.
But as you probably don't have "tracks" like that on a regular mixer, that would probably not work... Do you have something called "Stereo IN"? An extra input that you can assign to another input before it reaches the input mixer... That way you could send this "stereo in" to your track, and do that thing with the reverb and aux (like above) on your input channel.
Send all the other channels that the vocalist should hear to the aux as well.... If he wants to hear everything, you won't have to bother with the aux.... or Inserting the reverb either for that reason. Then just send to the reverb as usual and feed him the whole mix.
Hope this helps!
/Anders
