Newest update:
Last Monday, i ordered a new Breakout-Board at a German supplier. They confirmed my order and told me, it's on stock and delivery time 3-4 days. Nothing happend since then.
So today i lost patience and did some further tests.
Result is, i desoldered the 4 75ALS192 chips and connected all the S-/D- to the appropriate ports on the 50-pin connector. Had to change the direction of rotation, and viola', all systems running. Perfect...
Smoothly...
I can not wait any longer, to do my first print. I'm so exited....
Thank you all, for trying to help me with that issue.

Newest update:
Last Monday, i ordered a new Breakout-Board at a German supplier. They confirmed my order and told me, it's on stock and delivery time 3-4 days. Nothing happend since then.
So today i lost patience and did some further tests.
Result is, i desoldered the 4 75ALS192 chips and connected all the S-/D- to the appropriate ports on the 50-pin connector. Had to change the direction of rotation, and viola', all systems running. Perfect...
Smoothly...
I can not wait any longer, to do my first print. I'm so exited....
Thank you all, for trying to help me with that issue.

@dc42
OK, i'll try that.
Thank you so much, I will report if that works.
Meanwhile I finished cabling and everything works great , only the Motors

@dc42
Maybe this helps to localize the problem :
I measured the resistance between the different
Step- Ports:
X>Y = 9.74 kOhm
Z>Y = 9.74 kOhm
X>Z = 3.30 Ohm!!!
Maybe the Breakoutboard is damaged?
But i'm uncertain, because this measurements are always the same, no matter which combination of Ports 5-9 I use.
Not connected to the Breakoutboard the resistance
in each xyz combination is 7.75 kOhm (because of the common 5V line to each driver)

@jhonf441
No, not necessary and my drivers don't work at all, when connected.

@dc42
I hope you can see anything. I'm 100% shure, there is nö mistake in the cabling. I checked every single connection more than once, incl. with Multimeter.

@dc42

@dc42
I think you won't see much.

@dc42

To the question of groundloops...

is my power distribution ok?

@veti

hmmmm... now i´m unsure myself.... maybe dc42 can light this issue up?

@veti

not suitable for me, because i have no duex2 oder duex5 board. i have the duet2 ethernet and the expansion breakout bord. the breakout board is only connected by the 50Pin connector