I just got a sub for my desk setup.
Despite my dislike for Dynaudio I bought a Sub 9S because it was on sale and their specs are just ridiculous. It's a tiny little thing, sealed with a (supposedly) 9.5" woofer with a pretty short surround. Spec is 106dBSPL with 22Hz -3dB point.
The woofer measures 23cm (9") incl. the cage, so it would need 50mm Xmax (actual ~8" diaphragm) to reach their spec
That being said, I was actually positively surprised by the performance. It's good for what it is and definitely better than cheaper studio subs (like the weak KRK 10.4S that I know from a friend) despite its size and not being ported.
I'm sure max SPL is rather limited, but it will do what I'm comfortable with asking from it in my bedroom.
Actual -3dB point seems to be around 28Hz which is pretty good (just estimating by ear), useable in-room extension is ~24Hz in my setup. The crossover is a little (or lot) weird, it has either no, 60 or 80Hz high-pass to the monitors and then independant from that a dial for the sub low-pass without indications of frquency, so you just have to guess. I got it right on the first try, but it's still annoying.
I'm not sure why they wouldn't be honest or at least more transparent about their specs. The performance is good, no need to be untruthful.