Success! I removed the remote switch from the command center and connected it directly to the inverter with a new telephone cable. Still didn't work. So I did what any respectable DIY-er would do and I banged on the inverter with my fist a few times. Turned the inverter off and on and the remote switch of and on a few times and voila! The remote now controls the inverter! Except it's the opposite of what I thought I understood from the manual. The remote controls it when the inverter is ON, but does nothing on standby.
I checked the original cable again to see if it would work now, but it doesn't. And I don't want to fight with fishing a new one down under the coach and up into the command center, so I'm just going to run the new cable to the remote switch mounted on the side of the bed for access.
So, it was the cable, and perhaps slapping it around loosened something up.
BTW, Xantrex was no help. They basically just told me what the remote switch was.