Have you checked to see if the wiring is the same between the 512kb and 1024kb ECUs?
Wiring is same in most part, there are only small differences, a8 ecu is controlling 3-stage intake with 2 vacum solenoids while S8 ecu is controlling 2-stage intake with 1 vac solenoid. This i planned to use one to control both vac valves, just like S8.