Dave (Mad14)
We listened just yesterady to many amps on the B&W800D's which are a pig of a load (combined impedance and - phase angle), and the amp that won was the one that could double it's wattage for each halving of impedeance from 8 to 4 to 2ohms.
And the only one game enough to advertise this out of all the amps that you listed that do this right down to 2ohms, is the Classe Omega Omicron Monos.
Cheers George