sorry, why do you want to go back to 1.5.4 when 1.6.0 is fine?
Also, and I am speaking in general, Denon has not yet made public the 1.6.1 for OTA updates on the site, I don’t understand why one has to update right away.
It is always better to wait for it to become official.
Probably, the fact that the update to the new firmware has started, I think there has been some error in the system.