Elvis,
avaserfi makes an excellent point. Equalizer settings are dependent on factors that will not be shared between you and others here. In fact, the "optimal" equalizer setting can easily vary from one location in a room to another because of the effects of the room (walls, furniture, room treatments).
It's a good question to ask, but my advice is to use this information and set the equalizer so that the system sounds good to you. If you prefer to have the equalizer off, that's not a bad choice. The new Onkyo 805 comes with an auto-equalizer system, but I didn't find very quickly on the internet if the 804 has something similar. If it came with a microphone, it probably does.