Did the actual driver installation fail or with ‘no success’ you mean that the message about the USB Port being used is still there?
If it’s the latter, Grim pointed you in the right direction - the message is due to the hardware integration in Cubase: when Cubase is running, you can access the UR44 options from the Audio Hardware Setup in Studio Setup (formerly Device Setup) and DspMixFx is not accessible.
You don’t see this behaviour in SX 3 because there was no hardware integration (the whole UR series is much newer than SX 3).
Kind regards,