Ps. hopefully you marked the order that they went into the car...If not it will cause misfires, and random problems. Also according to SSP_268 2.pdf see link, (this is from memory) explains that the slave has a pin in the harness that makes it the slave (PS there are other W12 SSP's). I have also been told that the ECU's start out identical until they are married to the car?
https://www.vdveer-engineering.nl/en/information/vag-ssp/ssp-vag/ssp-vag-en/187-ssp-268-the-6-0-l-w12-engine-in-the-audi-a8-part-2PS. If you eventually figure out how to dump the EEPROMs I would like to know what makes them different!