I ordered the USB hub mentioned in this thread and just gave two controllers a go with it and can confirm it works.
Also, following the steps above, I only had to boot it once, but keep both controllers in line of sight of adapter.
I got two wireless controllers intermittently working. One controller tends to drop within a few min when both are plugged in. But I did manage to get both working when I follow a very strict setup.
First i made sure the adapter and controller firmware were both updated then:
Plug in adapter...