The 513 was, to me, one of the most interesting guitars to roll out of the PRS shop. Boasting a unique pickup and wiring arrangement, it allows for incredible diversity in selecting and splitting pickups.
With 5 single coils and unique wiring, the 513 is able to deliver everything from single coil twang to humbucker crunch, in 13 total combinations.
5 coils, with 13 different configurations, the 513 is my personal "do it all" instrument.
The 509 is the spiritual successor to the 513. They dropped the 3-way blade switch in favor of two microswitches, and lost 4 of the potential configurations in doing so.
The 3-way blade on the 513 allows a toggle between low output and high output humbucker when the 5-way switch is in a humbucker position. (5-way either fully forward, or fully rear)
So low/high for each humbucker selection are the "missing" configurations between the 509 and 513.
I'm not sure why PRS didn't see much value in that configuration, but it was dropped with the discontinuation of the 513 in 2017, and the introduction of the 509.
What do you think of the difference between Low and High output humbucker sounds? When I read that I figured it could be kinda of a gimmick that isn't terribly useful?
Does it work well as a simple substitute for a boost pedal?
I suspect the thing that would bother me is that I couldn't set the mode differently for each pickup. Like I might want the Neck pickup to be in High mode for a lead part but the Bridge pickup to be in Low Humbucker mode.
Two n-way blade switches would be awkward to keep track of for me. My first guitar was a Samick KJ-560 (HSS) and it has independant two-way on/off toggles for each pickup, and another two-way toggle to split the humbucker. I think that's easier to read at a glance.