How do you install a equalizer onto denon 3805 receiver?

Answer 1

Basically you don't. The usual way to add an equalizer to a sound system has always been to use the tape/monitor loop in/out which was transmitting every sound signal from the active input of the receiver to the equalizer. Than the equalizer would do is job of equalizing the sound before sending back the signals in the receiver prior to amplification. To my knowledge, almost no home theater receiver if any have had this kind of input in recent years.

You could still connect one source to the input of an equalizer and then connect the output from the equalizer to the receiver. This would not necessarily be a good solution given that: A) it would work for only one source. B) it would only work in analog so you wouldn't be able to experiment real 5.1 surround sound.

Good Luck