Thanks for the suggestion, I'll have a look, though at first glance I can't tell whether this is some sort of esoteric voodoo (remember the red transparent pens with which to paint patterns on a CD to get more natural music...)

I'm a bit disheartened that even the original Apple dongle effects this problem.

More details (and screenshot of the WiFi performance) here: https://news.ycombinator.com/item?id=13494910