Solved the issue.
1. install virtualbox (the same version) on desktop
2. created needed VMs
3. mount OS iso, install OS + vboxguestadditions (in Win I changed remote port to 900x and I activated remote settings)
4. power off VMs
5. install virtualbox and phpvirtualbox in DSM (with advanced features)
6. copy VM folders in virtualbox shared folder of DSM
7. launch phpvirtualbox and add copied VM
8. change display (port) and network settings in phpvb (bridged adapter with eth0 name and with all allowed)
9. optional shared foldesrs and virtual disks
10. start VM
11. me happy
if virtualbox stops sometime, don't touch "run". Doesn't work most of times. Restart DSM.