Not sure why no response to your question - maybe as it's Saturday, people are out running their systems!
I'm afraid I don't have much to help with - I went with the Apple USB to Ethernet adaptor to an Apple Airport Express. It wasn't all that expensive as such things go - here in the US the adaptor is $29 and the Airport Express was $99. One could also do a generic USB to Ethernet adaptor and then use a Belkin 600 router - that would be a little cheaper.
What sold me on the Apple solution was not only the pretty solid connection one gets, but ALSO you can take a 3.5mm stereo cable and go out of the Airport Express and into the M20d and using Airplay you can play music through the Line 6 system. So, not only can you control the mixer from the iPad, but you can play music as well, using the same wireless setup... THAT is way cool.
Coming from the Presonus digital mixer world, just getting the iPad to connect to the mixer was truly a pain -you needed a laptop with a firewire port - and it had to have exactly the right chipset to work consistently - My Core i7 Sony Vaio, the only laptop I could find with firewire 3 years ago had the wrong chipset - constant issues!!! Hooking the M20d up took me quite literally 5 minutes.
I was considering getting a WiFi dongle initially and read about some issues with them, and as you say, the list is a little old. Perhaps try one of the same brand as recommended and return it if it doesn't work.
Hope you get it to work - but I'd honestly recommend the Apple solution.
Let us know how it works out for you -