I just looked up the specs on the Onkyo-- it should drive the speakers you have proposed quite easily. You also might want to consider budgeting for some height channels as well with this receiver, since it includes the IIz ability.
One thing for your consideration-- some Onkyo's (not necessarily this one) have been cited before for having a bit of a brighter sound than say, the Pioneers. The Mythos speakers run towards the brighter side of things as well. This doesn't mean that they won't sound great with this particular Onkyo (If fact, my Z7 is very dynamic, but I love the way it sounds with my Mythos speakers), but an audition might be in order to see if you like the combo.
Good luck to you!