
Some previous owner had half-ass attempted to change out the PTB circuit to the lame Strat-style circuit. Luckily for me, he used the original potentiometers. I set about restoring the stock Legacy PTB circuit, and since I found diagrams for both the Legacy and the S-500, I tried both, and a mod of the S-500 circuit. I made recordings of each stage, so I could objectively tell the difference.
Some details: The pickups are the traditional G&L AlNiCo Legacy stock pickups. The recordings were done with the neck pickup selected, and all pots on "10." The strings weren't removed between each stage, so there's no variance there.
Here's the Legacy stock PTB circuit:

Here's the Legacy stock PTB sound file (mp3)
Here's the S-500 stock PTB circuit. Note the treble-bleed cap on the volume pot (C2), and the extra .001uF capacitor (C3).

Here's the S-500 stock PTB sound file (mp3)
Here's the S-500 PTB sound file, but this time without the C3 .001uF capacitor (mp3)
So, if you ever wondered how these different circuit mods sound with Legacy AlNiCo V pickups, here's your answer.
Conclusion:
I opted for the good old stock Legacy wiring, because it's brighter, and in combination with the PTB controls, provides the most variety. Notice how the S-500 circuit (designed for MFD pickups) doesn't sound so great with the AlNiCo V pickups! Using just the S-500's treble-bleed cap (C2) sounds pretty good, so that's an option.