A system based on the Kali speakers would have way more dynamic range that almost anything that your AVR could power. They are very accurate as well. However, that might just be a solution with way more dynamic range than you need. In addition, it won't decode Atmos, although you will still be able to listen to Atmos encoded discs- just not the Atmos channels.
So it depends on how loud you really like to crank it. If you are interested in a very wide dynamic range, I think the Kali + Outlaw system is still worth considering. But if you don't really listen all that loud, something like Canton would be just fine. By using the RXV-681 AVR's amp, you will be spreading that power to as many speakers as you hook up to it. So if you go to a 9 channel system, that amp's power supply is spread awfully thin. Not a big deal though if you aren't cranking the system loud.