In that PRS wiring the split line (in the BKP wiring green + white) is not wired directly to ground for the split but through a 2.2k resistor. In humbucking mode this connection is not connected to anything so it should not make a difference whether you use the resistor or not.
I have used this wiring on several guitars/pickups and have never noticed a change in the humbucking tone. I also have not noticed an increase in volume of the split mode. What I did notice was that any harsh highs, especially when used under gain, disappeared and that the guitar feels better to play under that condition. I would double check the wiring.
Good luck
Stephan