I used to deal with Denon for many years and I can tell you that when it came to a true lightning/surge damage, it was NEVER straightforward regardless of the AVR or AVC series. Almost always, the main problem is somehow related to the standby power circuit that is incorporated on majority of their receivers. As you have noticed, when it is plugged in to AC, the standby power is always powering the CPU in standby mode waiting for an on command.
Any surge, can do a LOT of damage within the unit---some of which may not be apparent at first.
I can literally write a book about the subject as I have seen my share of it. As a rule of thumb, if any of your valid supplies, is pulled down, get ready to find short(s). Anything in the CMOS switching or even a single port on main processor or EPROM etc. For example, any of the Mitsu. Mxx series or NEC UPDxx series of processors were easily damaged. Even if/when you get the unit operational, don't be surprise to see other issues down the road.
Denon has always had a High End moniker in the consumer audio. Certainly a refined look and perhaps better sound/features.
However when it comes to servicing, in my past years of experience, it has got to be one of the absolute worst, especially when dealing with lightning damage. As you will notice, control and power circuitry tend to be way over-engineered for basic tasks which can easily translate to nightmares.
Good Luck