Presumably you have a DI box to record a signal to begin with?
Subsequently, you'll need to check out the VST connections menu and activate whatever output of your interface you have connected the x-amp to, then set the DI tracks output channel to match in the project window.
Re: programming drums, hit F11 to bring up the VST instruments panel, insert your drum software of choice, then depending on which version of Cubase you are using, it will ask if you wish to create a MIDI track attached to it, or on an older version, you will need to create a MIDI track separately. If the latter is the case, again just set the output of the newly created MIDI track in the project window to the VST instrument you just inserted. I also recommend changing the MIDI map to a drum map to utilise the vastly easier programming method for drums.