So, I'm sitting here working on a computer in the same room as the receiver (SR6013), which is playing some jazz behind me, and it suddenly turns off at 1:20 am local time (a few minutes ago)...  
Surprised, I turn around and check it.  The unit's display says it's downloading an update!
I had checked my settings after seeing that we were potentially losing features with firmware updates, and so my setting for Auto-Update is OFF.  Yet the receiver downloaded and applied an update.  According to the unit, I am now running 3600-8280-1232-2065 and DTS Version 3.90.50.54  (I confirmed It has clearly already applied whatever update it received, it because it rebooted itself, and now when I run "check for update," it shows that it is supposedly up to date.)
While Auto-Update is off, "Allow Update" (some sort of master setting, as other settings disappear if you disable it) is set to "On."  Since I had Auto-Update off and Upgrade Notification on, I presumed I would be notified about updates and ASKED if I wanted them.  
I will turn off Allow Update.  Not happy.  Especially without knowing what was updated and what I either gained or lost.
Curious if others have had similar experiences.  In a way I want them to update for real bugs and for security updates, but I don't want to lose features.