How to connect a ROSS SYSTEM 15BAND 2 CHANNEL EQ

There is no practical way to hook it up. This model of Denon does not have pre amp out / power amp in connections. Therefore, there is no good way to connect it. A better model would have those connections, but this one does not.
Also the Ross EQ, made in Taiwan, imported by the defunct international music corporation, was not actually made for stereo hi fi use. It has 1/4" phone plug connections for PA systems. The audio level is much higher than a audio video receiver provides or receives.
So even if you bought RCA to 1/4" phone plug adapter cables, the audio levels would not match correctly, and there would be all kinds of goofing around, since there is no correct way to plug it into the Denon.
Sorry about that.

Tape monitor loop, perhaps?

That receiver has a tape out for some but not all of the inputs, and has another tape out for other inputs. And so because of the way that it is designed, not a very practical way to hook up the EQ, besides the levels being mismatched. You could do it but end up with a lot of hum and noise, it's not a hi fi eq, it was made for PA systems.