I have a similar problem ...
At a OMV3 (3.0.99) I am not able to install the Virtual-Box-Plugin.
I used the Web-Gui, installed omv-omvextrasorg 3.4.32.
When I try to add the omvextras-virtualbox 3.0.8 plugin, I get the following error message:
The following packages have unmet dependencies:
openmediavault-virtualbox : Depends: linux-headers-686-pae but it is not installable or
linux-headers-amd64 but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
I tried to add linux-headers-amd64 manual by apt-get ... but get following:
Hängt ab von: linux-headers-4.9.0-0.bpo.6-amd64 soll aber nicht installiert werden
E: Probleme können nicht korrigiert werden, Sie haben zurückgehaltene defekte Pakete.
I tried a new installation of OMV4 at a Test-PC and get the same error message.
How can I fix this problem?
Thank you for your help,
boh73