Hi,
With the AudioBox being digital hardware the levels coming into or out of it won't change when or if you change operating systems, it's pretty static. If you think you are suddenly getting less level out of your 44VSL it has to be software related, settings wise, a different setup in either your workstation or how you have the AudioBox configured internally.
We would suggest looking there, at how you are setup with your audio workstation and what may have changed from before in your monitor path in Cubase.