I don't own a Denon or bother with flashing firmware on HT components, but I can tell you that there is close to zero probability that the prior version is backed up so you can't simply revert to the old level.
You would have to obtain the prior firmware version you want and re-flash it. Perhaps the Denon site has older versions; if not you will have to hope that someone has the older version saved somewhere and can email it to you.