I've got a "R" series Yamaha from the early 80's as well. It's an R2000 rated at 150wpc. I bought it brand new along with a bunch of other classic pieces. They sound great with my JBL L112's. The only thing I've had to do is replace the STK's once. I also have a Fisher CA880 integrated. Another STK based unit. I've got a line on a McIntosh MC2500/C33 duo. Hopefully it all comes to fruition.
I've got that same Fisher as well. What is this STK you refer to?