Ok,one thing at a time.
First of all the 90% efficiency of the class D amps is usually at full power* .Then,lots of them are current limited.
From the layout and Amir's measurements it seems that it using a single board of the equivalent of 8 x 400a2 as the smaller sister does not do 400 W and it certainly can not do 800 W at 2 Ohm.
The advertised power (not the burst nonsense) seems to indicate to a custom,single board double PSU with some serious current abilities.
So no,is not like they threw the spare modules in there and that's it.
If they also took advantage of the chip abilities this should have,temp/clip/various amp condition indicators,amp and volt meters in real time,etc,the works,as any of the new icepower modules have.
I'm not certain about this though.
*Edit: and not the same efficiency at all loads,specially when serious current takes over .