I don't think you can do that, even the name suggests it, "emit a sound ( from a location )"
The only official way to do something like that is using the spk command
But, there may be a workaround, but i'm not sure if it would work..
One thing i was thinking was blocking the sound by hooking the emit sound forward ( if i remember right there should be something like that )
Another thing would be to use a specific channel, then for the specific players emit a mute sound on the same channel it should replace the previous sound...