Re: SONY DAV-DZ830W
I don't believe it works that way. You're stuck with it the way it is.
For example, my RCA STAV-3970 lists the db output, and it's range (volume) is from -94 all the way up to "0". It can only output 100watts per channel. It is only capable of going just so loud, have so much volume- then it can't go any higher.
The same will be for any amp/receiver. You're pretty much at your limit, I don't believe there's anyway to "unlock" anything... as the manufacturer would have had to have locked something first to begin with. And they usually don't work like that, to my knowledge. Though I could very well be wrong.