Usually, I don't think anyone would compare these two units to each other. The Onkyo '906 is really Onkyo's flag-ship unit, and to call it an A/V Receiver would be grossfully doing it a disservice. It really is a Network Receiver, hence the "N" moniker.
At this price, I would take the '906 in a heart-beat. I do like the Yamaha's, but really at about the same price, the '906 is definitely the pick of the two.
For absolutely grunt and scale for movies, the '906 has it. For warmth of music, probably the Yamaha, but really, at this price, the '906 is an absolute steal, and if you don't like it, I am sure that you can sell it in a few months for just about the same as what you have paid for it.
Just my opinion. I used to own an Integra DTR7.8 A/V Receiver (which is basically an Onkyo TX-SR875, but without some of the niceties, but exactly the same amplification-stage), and it was a cracking A/V Receiver, for the money. Heaps of grunt, and excellent for big-action movies!
Dan.