Below is a schematic (thanks Artie) that should get you either HB in series/parallel, either HB spin-a-split, both HB's split together in humcancelling mode in parallel, both HB's split together in humcancelling mode in series with ability to dial up to full HB's in series, and a tone bypass for added measure. The question is: what do you think will happen when the neck HB is put in parallel and the Master Series switch is pulled???