The wall mount Maggies are single driver, if I remember correctly, so no crossover to a tweeter. I might be thinking of another model though. They should sound really nice. They've got to be about 45 degrees to the wall and then you get more (mid/upper) bass than one would expect and a really good phantom center effect. But the sub really has to be on the same wall as the speakers due to the rather high crossover freq. Most subs have fairly slow rolloff filters, so setting the sub a bit lower in freq might avoid a nasty 100Hz bump.
The Hsu VTF1 MKIII would be a good choice but it's not small. It has a steep crossover filter and is easy to integrate.
I've done custom installs using Tannoy in-wall subs which would certainly meet your WAF requirements