the Ray 5 pickup is series.Another "problem" is that the SUB pickup has only two wires...
Apparently it is a little impossible to know if it is a Pickup That Is in Series or Parallel, Probably this is defined in the construction of the Coils!
As long as you have the money, your solution is simple.
Replace everything . The pickup, the preamp...everything.
It doesn’t matter which brand you choose to replace it with. (It’s your choice) They are all an improvement. Your best option is to find properly sized electronics and pickup that will fit the routs without having to remove wood.