Congrats on the RBH speakers. I have not heard these, but all of the RBH speakers I have heard offered a very clean sound with an especially (for the price-point) sweet/detailed midrange!
If you are saying you plan to upgrade to the A870, I would advise against it based on Gene's review of the previous generation A860!
The amp section was less than what it should be and the outputs from the pre-pro were weak:
https://www.audioholics.com/av-receiver-reviews/yamaha-rx-a860/conclusion
I would not gamble on these issues being fixed on the newer A870!
That said, you should be okay since you are running an XPA-5. The weak amp section won't matter if you don't use it and Emotiva amps (at least the early ones) always offered high gain which addresses the weak pre-outs.
Still, I would rather get something which could hold its own as an "all-purpose" AVR on the off chance you might decide to use the A870 amp section after all!