After extensive diagnostic measures I am rather stumbled upon a source of error - the caching behavior of Nero under Windows 8.1 is not compatible completely with the equipment and leads in certain circumstances (many small files on a SSD) to the fact that the program does not react for several minutes. Why this is so with these burners and other burners not me remains a mystery.
Solution: Creating an image file and then burn. And then do the things it properly in a reasonable speed.
Conclusion: The devices work (now ^^) do exactly what they want, they do it in a reasonable speed and acceptable volume. I am happy.
(And I have been so far, the devices to send back ...)
