Some companies go beyond certification. I don't think B&W is even bothered about THX. Remember, THX was started by George Lucas to push his Star Wars sound. There is an ulterior motive behind that certification. To a large extent it will (or may) suit movies. Music needs a different kind of sound generation. B&W has never pushed itself for movies, and has always been a music centric speaker.
You seem to like Onkyo speakers. If you have listened to them and like the sound, go for it. Comparing it to something else B&W in terms of company competence and technologies will not make much sense.
Cheers