Another Ka 9100 owner.. and I have gone into the unit to do some light repair. Best advice, label everything as you advance the diagnostic, there are loads of boards crowded into the unit.
My issue was the preamp stage and I am still seeking the right replace components, and will use some of the advice given this post.
For the earlier part of the year, I used the amp power side, and it had no issues and sounded great. Finally I got ahold of a Kenwood Model 9508 to temporarily put in my house loop. It works great though not as powerful.
Now the 9100 sits idle waiting for me to take the next repair steps.