Just sharing my findings here with interchanges with ECU's. i picked up a D3 A8 that was sitting in an impound lot and did not run for cheap. turns out it needed an ECU among other modules that where malfunctioned in the car. this car is an 05 and i have a donor/swap 04 A8 too so i robbed the ECU from that one, immo off and put it in the 05. it worked but i didnt want to rob peter to pay paul so i went on the shelf of ECU's and started digging around for something that might work. stumbled on a B7 S4 ECU that said it was also ME7.1.1 so i figured its worth a shot. read out the S4 ECU and compared the very beginning of the code to what i had extracted from the working 04 A8 ECU and they where identical! that told me that i had a shot with putting the A8 software in the S4 ECU because 9 chances out of 10 they have the same processor/hardware.i flashed the S4 ECU with the A8 software, installed in the car and not only does it run properly the car seems to run better than it did on the 04 A8 ECU! im starting to wonder if there are minor differences in hardware like with the MAF signal that bosch did to the S4 ECU to make them more aggressive?over all it was a neat discovery and really cool how the S4 ECU woke the A8 up!

i attached the B7 S4 and the D3 A8 BIN's for those who want to look at them. their just stock.