I'm not saying there are no single box solutions, I'm just encouraging you to consider your goals. What are you hoping to gain by stepping up to the 6700 or 8700. The 8700 lists for $4.5K. That's a lot of money for a receiver. If the main thing you want to gain with it is the rather...
There is no receiver in existence that has plenty of power and headroom when driving 11 channels. There's a reason they only provide, at best, a full range signal into two channels, or more often the completely useless spec of a 1KHz test tone. There is only enough power coming in to drive two...
If that is correct, it would completely disqualify the Onkyo for me, for the reason Greg explained. It's most beneficial to use an external amp for the front three channels, not just L&R.
However, looking at the RZ50, it does have pre outs for the front channels, so it really should be able to...