Welcome !
The fact that your unit is recognized by your Windows installation isn’t actually related to how Cubase deal with it, as the latter requires an interface ASIO driver to work with. So, in which way isn’t it ‘connected/recognized’ by Cubase ? In all cases, the first thing I would check is this (Studio > Studio Setup > Audio System pane) :
What do you have in the ASIO Driver setting ? According to the Rubix Reference pdf file, it should be something like ASIO Roland Rubix. If not, something has been missing during the driver installation.
This said, could you also post screenshots of the Inputs and Outputs panes of your Studio>Audio Connections window ?