Re: Kenwood KRF-X9992D
Speaker switch (A/B)
Tape loops (is the signal routed to go through a tape loop that isn't connected?)
Since it does it with all inputs AND the receivers tuner, one of two things are likely going on, as listed above. The third is also possible, but unless something catastrophic happened you would have known about is less likely is you blew the receiver.
I doubt this is it as you get some sound out of it, I suspect you hit a tape loop and the reason for the very low volume is the amp is only seeing what leaks through the preamp section.
If you can't find a tape loop, go into the set up menus and see what you find. You might want to call your friend as well, as he will likely know the receiver much better than you do. You can also call the company for possible help.
Ken Taraszka, MD