The caps on the amplifiers will probably need replacing.
As it turns out Bob, he was an electronics guy by trade & we had discussed him opening it up & checking the caps. In his passing the last thing on my mind had anything to do with this & wouldn't have asked. So, when I'm ready to set this up, it will be checked just because when I move this 55lb (amp) monster to where I want it's staying there period, thanks God the pre is only 25lbs.
To use your Yamaha HTR-5660 with your Pioneer Spec 1 preamp, you’d run an interconnect from the main RCA output of your receiver (the main output rca sockets are just above the left hand side of the speaker outputs), to an aux input or tape input on the Spec 1.
Another way to connect it so that you don’t need to use the Yamaha’s volume control, would be to run an interconnect from the Zone 2 output (and then Zone 2 operations on your Yamaha would be used), or the sound output from the VCR 1 or 2 outputs, to the aux or tape inputs. Try it and see which would be the best connection for you.
Don’t connect the speaker terminals of the Yamaha to an auxiliary input of the Spec 1. Apart from being electrically risky, the sound level will be far too high for the Pioneer preamp.