from what I understand the transmission BMW used for the Z4M is the same as the one from the 3.0si,
The E46 M3 transmission at the time wouldn't fit apparently so BMW used the si's trans,
The si transmission wasn't designed for the loads or revolutions of the S54 engine and that's why according to websites a lot of people have the 1-2 grind,
I have done it myself a few times when I first got the car, but now it seems I never do it,
Weird thing is, I can't actually remember what I do different
I am sure though a modified CDV valve will make the car shift a lot smoother, its a very noticeable difference