Hi you, I am really sorry, Db100. I cannot believe that korg does such a lousy job. Actually the manuals of the kronos say that usb audio works, so you might have the right to return the unit since it does not do what is promised (one essential function, iow. part of the contract, is missing). The Kronos is even advertised to work as a USB Audio interface for external connected sources - so… this HAS TO work.
But let us have a look at other options: Did you consider to change the USB-cable? Sometimes this is part of the problem. Another idea might be that some sort of setup in the Kronos is needed in order to make audio available on the USB-ports (just a shot in the dark from my side).
At any rate the issue is not at all related to Cubase, this is for sure - Asio4all works with cubase and if the Kronos is not seen by this driver the culprit is the Kronos. At any rate I would suggest you contact your dealer that sold you the Kronos in case you dont get useful help from Korg themselves (have you tried this?) - usually dealers have better contact to the manufacturers than we do.