I did push down on the back of the 3312 and I did hear a click and the broken channels then started working. Then all channels stopped working. Pushed again and got a click and back to the original center and surrounds not working but others working. Gave up, started watching TV and tried to switch from stereo to neo and lo and behold everything started working and has been working for more than a day. Thanks sancho for the advice. Clearly something is not quite right with this AVR and it sounds like mine is not the only one that has problems. I also wonder if I am getting full functionality out of all of the channels.
Anyone know if any similar problems have been noted in the Denon 4520.