I don't know how Denon manuals compare with others but they leave a lot to be desired.
My space is about half the size of yours. I have my 600 at about 10 o'clock with the sub channel trim set to -7 (it goes from -12 to +12), full and by-pass. I use a cut-off of 80Hz for movies and 60Hz for most music.
All of my speakers are set to small. My Denon has a stereo mode and a direct mode. In direct, all tone controls and processing (with the exception of the sub) is by-passed. In this mode, bass comes out of my 80s and my sub. I haven't been able to hear a difference between direct and stereo.
The advice that you will get from most of us around here is calibrate with instruments but let your ears be the final judge. It took me many, many months to properly dial in my system but I kept a lot of notes and learned a ton.
