The bench tests at sound and vision revealed a lot. You need an external amp with this receiver, if you don't have efficient speakers.
You know whether you need an external amp will depend on the individual's listening environment and needs right?
For comparison though, this Anthem is going to be less powerful than your 4520 whether in 2,5 channels or more, driven simultaneously. I am not a believer in the need of equal power in ACD but while it is always nice to have a beefier power supply, you get what you pay for so if more money is spent on the power supply, the manufacturer must cut back on something else. HK used to adopt the stronger power supply/equal (or nearly equal) ACD output. That, imo was silly because given a budget to compete with others, they ended up with less powerful amps (balancing the cost?) and therefore lower individual channel outputs. IMO, that was not a good thing in practical applications when very few people use AVRs for 5 or 7 channel stereo modes. For movies, not all channels will get the highest peaks at the same time.
I think Anthem is really smart with their flagship this time in using class D and less powerful amplifiers for the surround and ambient channels. That allows them to keep the weight down to a mere 32 lbs, probably the lightest 11 channel AVR available at the moment! The DAC chips appear to be the same as those in the Denon 4200 and Marantz SR7010, that is a notch below the flagship Denon and Yamaha AVRs, and the Marantz 8802 in terms of specs. That should not not be that critical because even the AK4458's specs should be enough to get it over the point of diminishing return so the final result would depend on the overall implementation scheme. The specs of the prepro section seems impressive. If the when the price drops below 2K, this will be a good replacement for my AV8801..