My big question: Must I have speakers connected to one of the monitor outputs to record? I plugged my guitar directly into the UR28M and could hear myself in the headphones (plugged into the headphone jack) but could not get any signal to register or record. I left the Monitor setting off, as I had nothing connected to the monitor outputs.
Must I have monitors connected, or am I doing something else wrong? Thanks!
You do not have to have speakers connected but, you do have to enable the audio track “Monitor” function to hear what you are recording and you need to disable the track “Monitor” function to hear during playback.
Also, if not already done, you need to create (in the Cubase>Studio<VST Connections menu, input tab) and assign (in the audio track inspector section) a mono input bus to your audio track.
Also, if not already done, you need to create (in the Cubase>Studio>VST Connections menu, output tab) and assign (in the audio track inspector section) a stereo output bus to your audio track.
Regards 
Excellent…thank you, Prock!