Are you looking at adding:
A: a wye ( a switch ) to lead into a stub or
B: a wye ( a triangular reversing module with 3 switches ) and one side of the wye (two of the switches) on the current reversing loop
C: some other configuration
Situation A should be a non-issues and could be feed with the power from the existing PSX-AR.
In situation B, I would have the switches coming off of the existing reversing loop be part of the current reversing loop, then the other two sides of the wye would be connected to one of my PSX's and the third wye (switch and and track attached to it) connected a new PSX-AR.