bar81, let me tell you 100%, no amp in can double it's impedance as you showed from 8 to 4 to 2ohms below. It's impossible as there are many losses. It would be like having perpetual motion which is a dream.
Cheers George
D'Ag does exactly the same thing. My M400s:
400 watts @ 8Ω
800 watts @ 4Ω
1,600 watts @ 2Ω
Cheers George