One of the long optical cables seems to be permanently kinked. It won't transmit data on channels 1 and 6. All the other cables seem to be ok, so it could have been worse.
Also, the 3x8 MIDI patchbay seems to be killing wall warts. They work briefly, then die. This suggests to me that it's probably time to get a new 3x8 MIDI patchbay, because until I do, Cubase recording is going nowhere.
On the other hand, I have patched the M-20s in directly, so that should work.