I was playing a couple over the weekend and, despite the differences in wood, a custom and a pro1 still sounded very similar to me. So I guessed it was down to either pickups or preamp. Pickups are a blunt tool when it comes to tone shaping, and because what I was hearing wasn't down to them or the wood, I reckoned the preamp has a bit of trickery in it. But I would need to test a passive Wal Pro in order to be sure.