It "works" but maybe it's not optimum. If you recall the history, the sub out was a late addition so maybe Andrew did the best he could with way he had. I hope I'm wrong and it's just your cable.

The rumour is the next Air will have a built-in 400W sub, 200W/channel 3-way with detachable speakers and tweetage on the back for omni-directivity; all DSP controlled.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated