I wish I had some more exciting update but it is still an update so here goes....
After researching I found out that you can connect a harness to the stock Celsior navigation unit to create an AUX input for both video and audio.
Once you remove the armrest box, it reveals an unused plug just behind the rear seat vent....
The little white socket is where the AUX harness needs to go in....just like this!
and once you add the harness it creates a new option on the VTR screen "VIDEO" in green (thank god I can still read a bit of Japanese...enough to operate the nav).
It was starting to look promising...I needed to test it out but couldn't think of a video source that I can bring to the garage...then I remembered an ancient portable DVD player I used to use when my son was young. It even had a super old Rugrats DVD still in there.
now the moment of truth....and success!
I also have the navigation safety feature override harness so the passengers can watch video while the car is in motion but I need to wire that all the way from the trunk so it will have to be another day.
I am going to split the sound aux input and run one to a bluetooth adaptor to be able to play music off of my phone so this mod worked out really well. I am now able to retain the clean stock look while modernizing the features of my car. I just wish I had found the info before I invested in a beat-sonic kit / non-nav climate control to do the un-nav conversion.