Tomek:
By the way, the pickups are not single coil and a humbucker, though they are shaped as such. Both shapes are actually humcancelling pickups - they have a single coil stacked over a dummy coil (no magnet in the middle). Alembic electronics are not cheap, but nothing else sounds like them. You can certainly experiment with using other brand preamps, but some type of preamp will be required. As for schematics and parts, again, I'd suggest you call Alembic and speak with Mica. She is extremely friendly and helpful.
Bill, tgo