Welcome to the forum!
Which Onkyo system do you own? If it has an auto set-up routine, have you run that? That might help with getting the speaker levels set correctly, and that could certainly help with the dialogue issue that you mentioned.
When you say that you get sound from your TV and surround sound speakers, do you mean that you have sound coming from the TV speakers at the same time as the Onkyo system? If so, do you want that (I wouldn't)? If that is the case and you don't want that, and you don't know how to fix that, just let us know which TV you have and we can look it up.