I've heard bad things about the Onkyos. Such as overheating issues and problems with the the video scaling. ( i.e. forced 4:3 on 480i sources and downscaling of 1080p over component)
It was enough to make me look elsewhere which I became interested in the Marantz. I've heard they have good audiophile cred and they don't have an on board video scaling chip which I prefer.