After some googling and finding the magic words “cd drive speed” got some hot hints even in this forum
so I tested it with great success on my cd drive. The audible difference between different speeds (I testet 1, 2, 4, the number behind the -x) and the time from the drive starting spinning until you hear music is hardly noticeble if there is one at all. So if something should be fairly trivial like gapless playback claimed here: Does Volumio 3 support gapless CD playback? - #2 by volumio
it would be the implementation of such a feature as an option for playback, if the claimed automatic here: Cd player speed issue - #2 by volumio
is not successfull
@volumio many thanks in advance! 
Cheers from Bavaria
Arnd
EDIT: since the carriage return in citing doesnt work: the magic command is:
eject -x 2 (or 1 or 4) /dev/cdrom
You don’t have to get eject beforehand, it is on the machine already
EDIT2: Unfortunately you have to repeat the command every time after a new CD inserted, because the ejection of the CD resets the setting (the commands name is “eject” after all 
). So an integration in the web interface would be REALLY appreciated. 