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!
When I had my REL connected to my Moon W6 mono blocks I connected the ground wire to my preamp. If I tried to connect the ground to one of the amp it caused a hum.
The wire from the REL only 3 wire. I now use an Aereal sub it has 4 wires for the high input.
Hi Drewhl
I have connected many subwoofer to speaker output amplifier the way you discribe in your post without any problems what so ever.
Where you could get somes difficulty would be connecting balance line level to single ended subwoofer imput.If you don't know what you're doing you get into some serious problems.
From my experience I never had any problems with speaker level connection.The advandage being that your your sub will follow and take the personality of your amplifier not a bad thing when you have an Ayre amplifier.

I also prefer having two subs in the room but that is for another day.
Good luck.
Thanks concertpiano!