unfortunately there's something missing in the Virtualbox-Installation-Guide under OMV v5.
The process of updating Virtualbox.
I always got the error of still running VBoxSVC daemon therefore I couldn't update Virtualbox.
1. Stop your VM's
2. stop Virtualbox-services under CLI:
3. Stop VBoxVSC daemon with:
4. find and kill other process
5. Update Virtualbox. I've downloaded the VB-package (.deb) and installed it via CLI
With these steps I was able to update Virtualbox
And to update the extension pack just follow the guide in the Guide-section by downloading
after that I're rebooted my OMV-server and everything was up-to-date