Unless Anthem has upgraded that receiver, it's still 7.1.4 so no dual sub capability.
I don't get the sense that Anthem is innovating any longer. It appears to me they've built some great products that are now in sustainment. I hope I am wrong.
Regarding power levels, I am elated with Axiom's transparent publishing of peak power for speakers and amps. Speaker peak power is 4 times continuous and peak amplifier power at 3 times continuous. The peak ratings are what really count. Axiom has its own methods for characterizing these levels but I really see it as a big failing of this industry to not come together and decide on a standard or at least, as a first step, a recommended practice, for peak power.
With regard to external amplification, for 5.1 and maybe 7.1, I fail to see why it's needed with Axiom speakers for both movies and music in a space as big as mine (4200 cu ft, 13' MLP). My 2012 $800 Onk has no problem. I'd expect the newer ones to be as capable if not more. That's not to say the Onk is as capable as the 1000 or 1500 but there is a practical limit and my ears-brain are at that limit.
With more channels, the equation may favor external amplification. Or, as Ian says, if you want to throw dance parties. And if you are like Slimpikins, who enjoys his Ts from 25 feet away while grazing, a 1250 or 1500 would do you well.