Unfortunately the M51 and M57 ECUs don't have much in common, nor do the engines really. Direct injection vs common rail, variable vane turbo on the M57, completely different autobox communication etc. Sure, they're similar blocks, but that's about it in my opinion.
The BMW 4.4 vs the Rover V8 is also quite a bit different, and can vary further depending on VANOS vs non-VANOS engines. The ECUs are both Motronic, but they're not the same era. Without looking into it, it would be a gamble if the autoboxes talked in a similar format, which is the issue I'm having with the M57 and Thor build auto ECU.
It's like my E60 - that's an M57 engine too. Albeit it is the TU2 version. But the ECU spits data out entirely differently from the original M57 - nothing lined up at all in our tests.
I hope to get back to this next year - I just have too much on the go at the moment. The V8 is holding on at the moment. Bigger irritations are water getting in via various places around the tailgate (and one of the rear load space windows?!) and the passenger blower again...
It did get a wash though the other day :)