Hi R DeVries,
Both your old Pioneer and your Denon are solid-state designs. Usually these have ruler-flat frequency response, even in the old days, so I doubt you'd hear any difference at all if you did a careful comparison, provided you didn't drive either receiver into clipping or close to it.
Those old Pioneers used huge amounts of negative feedback in the amplifier circuits to reduce THD (distortion) to 0.002% levels or less, an approach now frowned upon. The problem with the old Pioneer approach was that sometimes highly transient input signals could drive the amplifier stage into a kind of oscillation with audible distortion that sounded like nasty clipping. The phenomenon was identified by a Finnish researcher, Matti Otala, and it's called TIM (Transient Intermodulation Distortion). I was able to replicate it with a huge old Pioneer of the same vintage as yours. But it takes very high levels of transient input signals to trigger TIM.
Keep in mind too, that the tone-control circuits of those old Pioneers were never flat--i.e., they had errors that might boost the bass a bit or cause similar anomalies even when the controls were centered. When we lab-tested them the curves from the tone control circuits were never totally linear.
Regards,
Alan
