It was worth a bash, there must be some secret code involved although I don't understand how kaeru observed USB traffic when pressing those buttons.
Anyway I've hopefully got a nice FF/RW implementation that works during playback. Four levels of FF or RW scrub, press multiple times to step through speeds. If it works.
It's attached here, I at least want to get all the transport working nicely so that the ball is in NI's turf with allowing their customers access to the thing that makes their product what it is.
edit: I hadn't read the message above. That's great detective work and also frustrating because the magic key eludes us.