Hey guys, since i ran into that problem myself and the described solution worked for me
heres how to change the boot parameters in openmediavault/debian:
1. Get into a console either webbased or ssh (putty)
3. find the line which says GRUB_CMDLINE_LINUX_DEFAULT="quiet"
4. add your parameter behind the existing separated with space
5. save the file with ctrl + x
6. update grub with:
thx @bugnotme for this solution since i couldnt even track what happened on boot