The Denon AVR-S900W kept freezing. In once case, it powered off on its own (loss of video and sound), which is different than before, because previously when it froze, I could keep watching, and would only notice if I needed to use the receiver to change inputs, adjust volume, or power it off. This time, when I powered it on, the receiver came up in initial setup mode. It once again lost its settings! I figured the unit was faulty, and exchanged it.
I got a new Denon AVR-S900W. This one appeared to have the latest firmware from the factory, as it showed I was at the lastest version when I tried to update. I reconnected everything in the same way, and managed to get about 1 hour of usage before it froze again. This time it froze when I pressed volume up. The OSD for the volume level stayed on, so I had to once again pull the power cord.
I'll provide this additional information to Denon, hoping it will help them isolate the issue. But for now, I returned it and got a different unit from a different manufacturer.