I had those once but sold them.
Now i have, just for fun, a pair of 770.
Good top end, bass heavy...mids are off but after adjustment ok.
overall: good speaker
My Marantz model 500 blasting some serious Vac to the Klipsch (SB tuned) RF-7 mk1.
These speakers are dangerous was the comment i got from a friend.....LOL
Ofcourse not, it has no seperate headphone amp.......
Check all resistors on the main amp board to begin with, resolder everything, and i think with that you are almost home.
Best decks imo:
SD-930 (MAAC!)
SD-820 SD-720 All direct drive + level/bias computer
Forget the compudecks, beautiful but crap.
Best in that series is the SD-6000 or 6020 ( replace optocoupler may be needed)
5220 is also good but no external bias adjustment possible.
All i see is the component side.........what i'd like to see is the other side.....
So something like ''before and after.''
Example of my own work on a Kenwood supreme model 600: