A great way to route your effects to the P16-M would be to send the FX returns to two channels of the P16-M so the performer will have ultimate control over how much effect is in his or her monitor.
1. Route your channels and/or mix busses to the P16 as normal
2. On the P16 OUT tab of the ROUTING screen, select the channels you would like to send the FX returns to (i.e. P16 Out 15 and 16)
3. Under the Output Signal heading, select the FX return you would like to assign to those channels (i.e. DirOut Fx 1L and DirOut Fx 1R)
This allows for the effects returns to be available on channels 15 and 16 of the P16-M, which allows the performer to adjust how much of the effect can be heard in the monitors, if any at all.