That's where my confusion comes in. At some point there's still an external crossover. So wouldn't that need a chassis for the heat? Plus still limit the drivers to their desired ranges?

I also believe that the ADA Amps are Axioms own specific custom design. Around the time I became an Axiom customer 2013/2014 the blog had some in depth articles and some you tube vids. regarding creating their own design and the differences of typical class D and the ADA.