I own an Integra DTR 7.1 reciever, while I am not familiar with the one you are interested in, the general difference is that the Integra is built with all top quality internal components. The chips, resistors, capacitors,etc are all higher grade and higher accuracy(tolerances are closer). Usually it is not a features or power issue but a quality issue.
I've heard that about the quality of components, tolerances, etc. I think that the Integra also supports A-Bus whereas the Onkyo doesn't.