To see how different these two transmissions are, I suppose I could go read and compare the ZF parts lists for the ZF 5HP-24 and the ZF 5HP-24A, the former being for RWD cars, and the latter being the variant used for the Audi Quattro.
However, news of a big-picture mismatch would mean I needn’t bother. So far, such news hasn’t been forthcoming.
The Jaguar XK8 uses the ZF 5HP-24 and the contemporary Audi A6 with the 4.2 liter V8 uses the ZF 5HP-24A. I’ve been comparing their technical documentation as to the truth tables for the various valves and how they affect the various internal brakes and clutches. My conclusion: identical.
So, worst case, if my Audi has a bad solenoid and a new one would break the bank, or if I just wanted to learn more, then I could hypothetically go buy an old ZF 5HP-24 and strip it for parts. Finding that is a lot easier than finding the ZF 5HP-24A version as in the Quattro, and if the internals are the same except for the 4WD aspect, then yay!
Not that Jaguar XK8 cars litter the junkyards locally, but BMW E38 cars do, and this was the transmission of choice for the 735i and 740i cars.
My life just got a lot easier.