I'd have to see the schematic to be sure but I'm guessing it's not a Darlington pair. I can't see in the spec but I'm guessing it's a class AB or similar with the transistor pairs (PNP and NPN) in parallel for the failsafeing.

That being said, it would also be possible to build a class A amplifier with two Darlington pairs, using four transistors. Of course then the transistors would have to be biased active which means you could cook on the amp whenever it's powered.