Thanks for that. I was told by others that the Denon would work as a power amp. No, I don't want it to work as you have suggested. I would like to use the Denon purely as a power amp.
So there is no way of using the Denon as a power amp then?
You cannot use it purely as a power amp, unless you open it up and rewire it. You can use it as markw stated, with your new preamp running into an analog input on the Denon. You then can select "pure direct" or whatever Denon calls it, to bypass most of the processing, but you are still running it through the preamp section (which you will know from the fact that the Denon volume control would affect the volume).
There is really no point in doing that, unless there is some kind of special input on the new preamp that is not on the Denon (like a MM phono input, if one is needed). Basically, you will be adding needless circuitry to the signal path, and will degrade the signal. Perhaps not audibly, but it won't be making it better.
The Denon is simply not designed to be used solely as a power amp. That is why the manual does not tell you how to do it, because you can't.