Balance Amplifier to Subwoofer connections

I am intending to hook an Ayre, fully balance amplifier to a subwoofer via the high level (speaker) inputs. Ayre has told me NOT to connect negative to black but to chassis ground. A balanced amplifier cannot be connected to anything with a common ground.

The subwoofer amplifier manufacterer (O-Audio) says the plate amplifier has no common ground by virtue of the fact that it only connects 2 prongs to the outlet.

I have also heard that other audiogoner's have connected Ayres to subs via the red and black speaker connections without a problem.

Can anyone explain to me in more detail what is up with this technically and what connections I should be using.

Additionally, can you tell me the pros and cons of connecting the speaker leads to the sub from the speakers vs the amp. Does it have to do with length, noise, etc?

thanks to everyone in advance!